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No.
37
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Pumice and other extraneous volcanic materials on c o r a l a t o l l s
M.-H.
Sachet~: .
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Issued by
T'IIL PACIFIC SCS'ENCE
BOARD
National Acadelriy of Sciences--~atio:ial Research Council I~Jashington,
D.
C.Nay 15,
1955
Introduction
Pumice on c o r a l a t o l l s
Geographic d i s t r i b u t i o n
Probable o r i g i n and t r a n s p o r t Chemical and p e t r o l o g i c a l n a t u r e Uses: a g r i c u i t u r a l and abrasive Ecological. significance
Other noncalcareous rocks, occurrence and uses on c o r a l a t o l l s
Imported s o i l on c o r a l a t o l l s Conclusions
Addenda Bibliography
Page
1
1I.
5
1 0 1 2 3.2
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Pumice and other extraneous volcanic m a t e r i a l s on c o r a l a t o l l s
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'' by
. . . . . . .I'arie-H&l&m Sachet . . . . . 8
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Introduction
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"Every square inch of land i n t h e a t o l l i s ooral. ..
,...,"
Wood-Jones, (1910, p
,
5 7 ) . Sta-L-ements s i m i l a r t o 'tKi,s, varying only in t h e i r' . oolorfulness,,,accuracy, o r d e t a i l , together With variou.s. g e n e r a l i z a t i o n s t o t h e e f f e c t t h a t a t o l l s : . a r e hlade up e n t i r e l y of :or2anic limestone, a r e
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abundant through the: litera-Dure - of c o r a l islauds; ' in d i a r i e s , adventure s t o r i e s , m d s o i e n t i f i c reports; and within a e r t a i p l i m i t s such statements
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, .. . . . . . ,.:
%re t r u e ..,:i: ... : ,: . . ,
, . . . , . .
. .: The 'presence on a t o l l s of v o l c a n i o r o c k s such a s pumice and . . .
b a s a l t , a s well a s volcanic SoiXs;. has &roused much c u r i o s i t y and i n t e r e s t .
. . . . . .
The most conspicuous and abundant foreign rock i s pumice. Examina- t i o n of t h e l i t e r a t u r e reveals i t s . p r b s ~ n o e in widely separated islands and shows i t s importance a s a "natural resource'.'' We w i l l f i r s t , c i t e a v a i l a b l e information on pumioe, i.ts occurreace, uses, sj:gnif ioance, and complete :
t h i s record with mention of other extraneous materials. For t h e purposes of t h i s review, p w i c e i s taken t o meaa volcanic e j e o t a t h a t a r e o e s i c u l a r and ligint enough- to' f l o a t . Thk awbhor i s aware t h a t rookg of s i g n i f i c a n t - . l y d f f f e r e n t ts-xture and .chemical composition may be included, a n d - t h a t t h e
petl'ologist might desire..:further- restriction of .the t e p i , which
Ss.
impractic-.
' a1 here. . . . . . . . . . . .. . . . .
. . Geographic d i s t r i b k t i o n
. . .. ..:Seurat '(1903,p. 61, who spent m a y months in t h e remote T u q o t u
, , ~ ' i o l l s a n d the neighboring Gambier .Islands, r e p o r t s t h e presence of small ' p i e c e s .of pumice on the. beaches of South Marutea, one of t h e e a s t . e & o s ~
' a t o l l s of t h e P a c i f i c . Pumioe i s n o t often reported from t h e Tu&.otus,, and i s indeed probably not a s common t h e r e a s i n various c e n t r a l P a c i f i c groups of a t o l l s ; however, the l i t e r a t u r e an t h i s immense archipelago i s
. . e s p e c i a l l y poor and inadequate.
Cn t h e contrary, pumice i s reported by many o%sorvere i n many d i f f e r e n t i s l a n d s in t h e c e n t r a l P a c i f i c and i n t h e Iviicronesian A t o l l s .
Van Zwaiuwenburg (1941, p. 1 5 ) found.- it okkanton i s l a n d , and., , W . A. Dixon (i877, p. 165) s a i d it was abundant'on'~1dalden Island. I n 1862,
'W.'W. G i l l , a missionary, was c o l l e c t i n g i d o l s on Pukapuka (Cook I s l a n d s ) and wrote (1876, p. 60): "One old man w a s oarrying what seemed t o be - a l a r g e lump of coal with evident ease. . . T h i s -'tGrnedout t o be pimica: stone
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blackened by iong exposure t o r a i n - a n d wind?" This piece was d e p o s i t e d . b y . . . G i l l . . in t h e museum of t h e University.of sydney; . . . . . , . ? . , . . . . .
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The U. S. Exploring Exnedition (183G-42) observed pumice i n several of t h e many a t o l l s v i s i t e d . Dana (1549, p. 77) mentions it on Fakaafo and Howland. Of t h e l a t t e r he say6 t i a t b i t s pf pumice and pieces of driftwood a r e s c a t t e r e d a l l over the i s l a n d ' s surfa.cer
The abundance of t h i s pumice a t times is extraordinary. Nhitmee (1878, p. 108) wrote t h a t in t h a t year, ships met g r e a t q u a n t i t i e s of it in t h e vioinj-ty of the E l l i a e group, and quoted newspaper accounts t o t h i s e f f e c t . lie added:
"...
t h e shores of a l l t h e E l l i c e I s l a n d s a r e thiok w i t h it. Hundreds of tons have been t l i r c m up on each island." An i n t e r e s t i n g n o t e here i s t h t l t t h e p m i c e wimn f i r s t observed (April 1878) was f r e e ofsea-weeds and barnacles, but these were c o t i c e a b l e by June.
. .
.&other important record of pumice in the E l l i c e I s l a n d s i s t h a t of Hedley (10.96,
5.
1 6 ) from Funafuti: "E$e.r,phere mall pieces of pumice t h e s i z e of a walnut might .be collecked on t h e . b a h I % e s . The n a t i v e s say t h a t a few years ago muoh pw.ice erne ashore, coinoident with which t h e f i s h fromwithout t h e lagoon became u n f i t f o r food.". Finsch (1914, p i 43) says t h a t he himself saw g r e a t q u a n t i t i e s of pumice on the s t r z n d a t B u t a r i t a r i , Gilbert Islands. P. E. Cloud, Jr.
(1952, p. 21) observed and collected it on Oaotoa in t h e same group"
. . . . .
There a r e few records of tb.e presance of pumioe in t h e Narshall
~ s l a n d s . Cne of these i s by Chanisso (1621, p. 156), one of t h e most
g i f t e d and versati1.e n a t u r a l i s t s t o v i s i t P a c i f i c a t o l l s . Another reference i s by Orunde~r~ann (1887, p o 442) on Ailuk. S t i l l another i s by Stone (1951, p, 2) on Arno Atoll. I t i s q u i t e possibl.e t h a t pitnioe does n o t reach t h e s e
isl.ands a s o f t e n or a s abundantly as it does t h e Gilbert o r E l l i c e I s l a n d s . However it i s ?resent now in t h e Marshall I s l a r ~ d s , wid F , K. Fosberg
observed it in 1951-52 (unpublished) during t h e blorthern Marshs.11 Islands Expedition. During t h i s in?estige.tion pumice of several d i s t i n c t s o r t s was noted, and s p e o k e n s were c o l l e c t e d on Pokak, U t i r i k , Ailuk, Jemo,.
Kwajalein, Ujae, Totho, and Ujelang a t o l l s . I t v i m o r d i n a r i l y found a s s c a t t a r e d pebbles, u s u a l l y w a l l , but l a r g e r pieces up t o t h e s i z e of man's head a l s o were seen. It occurred in g r e a t e s t q u a n t i t i e s inland on t h e sur- f a c e of the ground on Kirinpan I s l e t , iJjelang, and on Ebeju I s l e t , Ujae.
On Ebeju perhaps a bushel could have been gathered in ar. a r e a 20 meters square. This was a l o c a l i z e d occurrenoe, though; other simil.ar a r e a s have l i t t l e o r no pumice. Nuoh smaller amounts were s c a t t e r e d on t h e beaches, a s on Jemo, above t h e normal wave mark; and i n several places where dunes and sand s p i t s were being c u t away by wind or waves, buried pieces were exposed.
The only record of pumice i n the Caroline a t o l l s i s from Kayangel Atoll, Palau (Cloud, personal comunica.l;ion, 1953)efiut s e e Addenda, p.2$.
Several records of t h e presence of pumioe a r e a v a i l a b l e from Laysan Island, one of t h e northernmost a t o l l s in t h e world. H. H. Schauinsland, who spent 3 months on t h i s i s l c a d i n 1896, observed hard seeds, nuts, masses
of r e s i n , and rounded pieces of pumice / r ' ~ h s t e i n ~ i n t h e abundant p i l e s of b i r d droppings (Schauinsland, 1899,
p.
20). I n an appendix (p. 89) he enlarged on t h e subject and noted t h a t he did not f i n d any pumice on t h e s t r a n d during h i s sojourn, but t h a t it was always present in the c e n t e r oft h e island, p a r t l y on t h e surface, and p a r t l y in t h e guano p i t s . An i n t e r e s t i n g sequel t o t h i s report i s found in t h e journal of blunro (1946, p. 43). Quoting from h i s journal on Laysan (June 20, 1891) he writes: "On t h e dry surface of t h e lagoon t h e r e a r e l o t s of small pieces of pumice,"
but adds, "evidently t h i s was c u t t l e f i s h bone disgorged by birds." He r e p o r t s f i n d i n g pieces of c u t t l e f i s h bone in t h e gizzards of young alba- t r o s s e s and other birds.
It would seem t h a t the two observers may have seen and reported t h e same thing. It i s i n t e r e s t i n g t o note t h a t t h e y both believed it t o be pumioe a t t h e time. Since we have no idea what r e g u r g i t a t e d o u t t l e f i s h bone may look l i k e , it seems d i f f i c u l t t o s e t t l e t h e question a t t h i s point.
It i s urfortunate t h a t no one thougMof bringing back a b i t of t h e material.
However, it i s q u i t e possible t h a t M r . Munro should n o t have d i s t r u s t e d h i s 1891 observations and t h a t both he and Schauinsland d i d observe pumice s c a t t e r e d on Laysan. The f a c t t h a t some of it had gone through t h e alba- t r o s s e st stomachs does n o t n e c e s s a r i l y mean t h a t it was n o t pumice.
Schauinsland (1899, pp. 20, 89) remarked t h a t these b i r d s w i l l s~.vallow any- t h i n g and t h a t they may pick up the rounded pebbles i n t e n t i o n a l l y "to help t h e i r digestion."
Nuch l a t e r ( i n 1912) Elsclmer v i s i t e d t h e Leeward I%waiian Islands and recorded (1915, p. 35) pumice on Laysan, P e a r l and Hermes F.eef, Lisianski, and Dniiway.
One of tho most i n t r i g u i n g observations of pumice i s t h a t made a t t h e time of t h e v i s i t of t h e Austrian ship Fovara i n 1858, t o t h e a t o l l of Sikaiara o r Stewart Island. Both Scherzer (1862, p. 607) in thel'Narrative"
of t h e voyage, and Hochstetter (1866, pp. 157-158) in t h e "Geology," men- t i o n t h e abundance of pumioe on Faule, one of t h e two l a r g e r i s l e t s of t h e a t o l l . Hochstetter pointed out t h a t the pumice was " f i n e l y porous and brown, and f l o a t s on water." Trying t o a s c e r t a i n t h e thickness of t h e pumice beds, Hochstetter examined t h e s i d e s of a water-hole about 1 8 f e e t i n diameter, found in t h e middle of t h e f o r e s t . The rims of the hole were of "compact c o r a l conglomerate," and t h e pumice l a y a l l around but only s u p e r f i c i a l l y , i n t h e hmus l a y e r covering t h e o o r a l rock.
Guppy (1887, p. 140) mentions t h a t during the surveying voyage
of t h e "Fly" much pumice was found i n various places along the e a s t e r n coast of Australia. This i s reported by Jukes (1647) in h i s n a r r a t i v e of t h e voyage. The "Fly" v i s i t e d a low ooral islend, Raine I s l e t , and Jukes
(1847, p. 128) observed pumioe there, embedded in the o o r a l sandstone form- ing t h e island,
Beyond Australia, westward i n the Indian Ocean, we f i n d pumice recorded i n the Cooos-Keeling I s l a n d s by s e v e r a l authors. The e a r l i e s t
such reference i s by Keating (1840, p. 378) who said: "Large q u a n t i t i e s of pumice-stone have been found on a l l t h e islands." Later pmioe was recorded by Guppy (1889, pp. 284-28?), who spent t e n weeks on Cooos-Keeling in 1888, and by Wood-Jones (1910, pp. 170-171), who l i v e d f o r f i f t e e n months on the main a t o l l as a dootor and included h i s observations in h i s book "Coral and Atolls. "
Further west we have reoords of pumioe from t h e Chagos Archipelago:
Xoresby (1844, p. 309) wrote: %lasses of pumice-stone a r e oonstantly found
-4-
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on t h e beach of t h e islands,
. ...'
One'.' $iece i n Captain Moresby's posses-:
sion, measures 37 by 27 i n c h e s , a n d 8 lbs. 1 2 02." Finsch (1887,'
.
p. 42) and Wilson (1889, p. 144) observed pumice i n 1884 on the beaches of Diego Garcia in the same group.The l a s t region i n t h e Indian Ocean from which we have records of pumioe i s t h a t of t h e long c h a b of a t o l i s of t h e Maldive and Laocadive archipelagoes, Because. of the!-r proximity t o India, of t h e a o t i v i t y of ' t h e B r i t i s h c i v i l servants, Navy o f f i c e r s , and n a t u r a l i s t s , and b e c a ~ s e several great s q i e r i t i f i c expeditions studied these islands, we have more information on thavlthan on most a t o l l s , and those s c a t t e r e d in time.
I n 1892-94, s: party on t h e ship "Investigator" surveyed t h e
Laccadives, and Albock (1902, p. 1751, a n a t u r a l i s t on t h e 1892 campaign, r e p o r t s t h a t two of , t h e s h i p ' s o f f i c e r s discovered a bed of pumice a l i t t l e inland of t h e north eud of Cardammi (Kardam8.t) Island. Unfortunately, he did not hear of it u n t i l the ship had steamed away. Oldham (1895, pp. 6-7) mentions t h i s occurrence and seems t o imply t h a t he himself saw t h i s pumice
bed, but apparently a t a l a t e r date. "The northern point of the i s l a n d i s formed by a s p i t of sand on whiah I found a q ~ e t i t y of pumice,. extending inland f o r about f i f t y yards from t h e extreine point; it i s
strewn
a l l over t h e ,surface, and v a r i e s in s i z e from a marble t o h a l f a f o o t @ diameter."The "1nves~tSgator" p a r t y a l s o found pmioe pebbles on t h e bo-kbom of t h e Bay
of Bengal (Aloock, 1902, p. 153). . . . .
. . . . . .
. E l l i s (J924, p. 9) recorded pumice from t h e Laccadives. , I n 1899- 1900, J. S. ~a.r&,iner v i s i t e d the Maldives, Miniooy, and ,tne h c o a d i m s , and w 3 t h h i s two~.assooiate s, g a t h e r e d v a s t mounts of irif;o&ation and ex- t e n s i v e zoological and botanioal c o l l e c t i o n s . The resu$ts f o r t h e main p a r t were included i n two Large volumes published i n 1901 t o 1906. Gardiner
(1906, pr 582) found p m i c e on many of t h e a t o l l s . I n another paper ( W i l l i s and Gardiner, 1901, p, 113) Gardiner mentions f i n d i n g a l i t t l e pumioe among foraminifera1 sand on Euleie Island, Male Atoll. Soon a f t e r
Gardiner, A!.exander 9 g a s s i z v i s i . t e d t h e Maldives (1901-02) and published h i s account, acccmpanied by a volume of valuable photograwhs (1903 b). He recorded (op. 63, 69) tne presence of abundant windrows of prmice on t h e beaches of two a t o l l s , South Malosmadulu (Embudu islet) and North Xalos- madulu (Uedu I s l e t ) .
,. ' . ... The. l a t e s t information o n pumioe i n t h e 'wialdives was oollected~..:,.
during
,.tits.
John Nurray Expedition of 1933-34 and i s recorded i n Sewell' s acoou&s. On Ilorsburgh A t o l l (Sewell, 1936 b, p. 116) l i n e s of small pumice fragments were observed on t h e sandy sea beach o f . Goidu I s l e t .. . .
.
. . :.. ,.:On Addu
toll
(Sewell, 1936 a pp. 77, 79, 82) pumice occurred on seoer&of . . . .. t h e i s l e t s ( P u t a l i , Nulikadu, Naradu) inland from t h e sandy lagoon. beaches.. .: On. P u t a l i (p. 77) "Rwning along the whole l e n g t h of t h e northern p a r t af t h e island, about 10 yards t o t h e e a s t of t h e ateep bank t h a t no8 forms t h e e a s t bank of t h e lakes Lrelongated ponds running polrallel t o t h e lagoon edgeJ t h e r e i s a well-marked l i n e of rounded, water-worn pieces of pumice." Sewell goes on t o quote Gardinerrs and Oldham's observa- t i o n s , and concludes that t h i s pumice must come from Krakatau: " i f t h i s be so, t h e n since 1885 o r thereabouts the inner beach of t h e i s l a n d has ad- vanced towards t h e lagoon by some 1 0 yards, and sand s p i t s have been b u i l t c u t i n t o t h e lagoon and have cut off t h e lake. ,. .
I tNo records were found of t h e occurrence of pumice on t h e Western Inrlia'rl Ocean a t o l l s .
Very l i t t l e i n f o , m a t i o n ' i s a-vailable on the a t o l l s and l a v c o r a l islands of t h e Gulf of Nexico'al?d t h e Caribbean Sea, and t h e r e a r e n o . .
records of pumice on them.. .
o ow ever,
. . . in t h i s oonnection, it i s i n t e r e s t i n g t o note t h a t Guppy (1917, p. 6).melsttions pumice pebbles found i n beach d r i f t i n . t h e . West Indies.. .
Probable o r i g i n and 'mwispor't
Although t h e ocbur~ence of pwiice on coral. a t o l l s h a s , a t times, g r e a t l y puzzled tiie observers
--
e s p e c i a l l y when found f a r inland on t h e i s l e t s--
it has been generally accepted w;.thout argument t h a t the pumice had been f l o a t e d by t h e ooean a f t e r eruptions' o f distaink volcanoes, c a r r i e d about by currents, and deposited on:the beaches of i o w islands , i n t h e same manner a s other d r i f t material..Elschner (1915, pp. 35-36) w o t e :
'We can produce tvo sources of t h i s pumice i n t h e . . l a s t decades. Tha Sunda Straigli* sustained groat changes
a t tha time of t h e eruption of t h e volcano Krakatoa, a s imtnense q u a n t i t i e s of pumice stone were thrown out, whioh were then washed asbore on tho r e e f s and beachesof t h e
d i f f e r e n t c o r a l islands i n t h e o e n t r a l PacificOcean; f o r inst'ance, cn Nauru, a l l over the lv1arsI:all Islands. and the MortAock a t o l l s , etc., a l s o in t h e northern p a r t of t h e
Pacif i c y pumice stone pieces, even though small q u a n t i t i e s , were found d r i f t i n g and washed ashore.
"In t h e year 1906
...,,
Captain Schlemmer a t t h a t time in charge of t h e phosphate works on Laysan Islanc?(which have since ceased t o e x i s t ) mentioned ia h i s d i a r y t h a t he observed t h a t a quake 'Jas t o be f e l t and on the following days t h e sea was f u l l of d r i f t i n g pumice stone pieces. On h i s t r i p from Laysan I s l a n d t o Honolulu he observed t h e s e pumice stone pieces a s f a r a s i n t h e neigh- borhood of t h e main group near Kauai.
"4p earance inland
d---
Seabirds, e s p e c i a l l y f r i g s t e birds, during t h e i r
f l i g h t , pick up f l o a t i n g p a r t i c l e s on %he water w.d swallow them, s o t h a t t h e discover:^ of t h e pumice stone i n the i n t e r i o r of tiie i s l a n d i s t o be e x p i a j l e d on t h e p r i n c i p a l t h a t un-
doubtedly t h e b i r d s vomited these pieces.
. . "The appearanoeof pumice stone in t h i s neighborhood ,in March and April, 1906, is i n t e r e s t i n g ; it documents t h e l a s t t r a c e s of volcanic a c t i v i t y , ;'lhich formerly were
, . , here o f an imposing degree. A t t h e mentioned time erup- t i o n s of t h e Hawaiian volcanoes d3.d n o t take place. and t h e occurrence of d r i f t i n g stone, l i m i t e d t o t h i s p a r t of t h e group, was t h e r e f o r e of a l o c a l nature, t h a t i s , it most probably was caused by a quake of t h e ocean bottom
i n t h i s neighborhood."
Yamanari (1935, ,p. 17) report's t h a t a f t e r
the
eruption of a submarine voloano i n 1934, l a r g e $ e l l t i t i e s, of p.m5&-drifted around in t h e s e d s n e a r the Einmi-4atsuma isl&:nds.. . . ! ~ . . .. .. . . . .. . .
The great q u a n t i t i e s of pumice found on'~ik.ka.ana a r e perhaps. . ,
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more e a s i l y explained than i f t h e y occurred in t h e Tuamotus, f o r exainple.
SiFaiana, ,a seldom described a t ~ l ? ? , ~ . l i e s 'near many volcanoes, those of Eew BBrtain;the Solomon Islands, and t h e ~ a n t a Crwz Islands, t o mention
theneare$$.ones. Whiohever of' t h e s e t h e p v i o e . , o q e from, it did not have, t o t r a v e l very f a r and oould .W throwfl qp on, t h e i s l a n d s when
g r e a t qu&ticies af it were s t i l l . . . . .float5ng , tog&tbe2r, before being s c a t t e r e d over g r e a t e r expanses of t h e sea,
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. .
The question of how f a r and how lope; (p&ce can f l o a t was tairen up by 11. B. Guppy. Ee was f a s c i n a t e d by t h e f a c t o r s responsible f o r t h e d i s p e r s a l of p l a n t s ; t h e r e f o r e he t6ok g r e a t i n t e r e s t in the study of ' d r i f t m a t e r i a l and wrote two books on t h e sv.b?bject. I n another of h i s works
(Guppy, 1887, pp. 137-144); he devot66.a whole chapter t o the d r i f t i n g of pumice q u o t b g many of the .$ourcesmerrt;ionedhere and. giving much informa- t i o n on .@e presence of puniice on h i g h - island b@ch6's"alid- . . . at. sea.
. .
. .
< :
~ . . . "The p w i c e e j e c t e d during t h e volc&ic outbreak a t
Blanche Bay i n New B r i t a i n in Nay,. 1.878, & i s c a r r i e d e a s t - ward by t h e d r i f t - c u r r e n t s , and 1 i t e r a l l y d e S u g e d t h e shores
of the Solomon Group, both impeding. n a v i g a t o n : ,. . . and 'Cenlporarily suspending t h e beche-de-mer f i s h e r y
, . . . sr.
Wilfred Powell, who was present a t t h e time of the eruptfon'ui
Ne+riBritain,s t a t e s t h a t Blanche Bay and a great p a r t of St.' Geor-gels Channel were s o t h i c k l y covered with pumice t h a t it was im-
possible. for-, . . a . boat o r even a vessel t o work i t s way through - .
. . . .
, . . .
"Several agencies a s s i s t i n t h e dispersion of' a . f i e l d of f l o a t i n g p&ice. I n t h e f i r s t plaoe, t h e t r i t u r a t i o n o r wear and t e a r of t h e f r a g e n t s , a process by which :tney soon
obkain tho form of rounded pebbles, considerably reduces
.
.t h e i r s i z e
. .. .
I n t h e oourse of time the &in& and waves s c a t t e r t h e f l o a t i n g fragments, and arrangeYthem in long s t r e a k s a mile or more in length and..goqe 25 o r 30 yards i n width....
F i n a l l y....
s o l i t a r y fragments ' a r e s c a t t e r e dover the s u r f a S , o f t h e ocean.ivhere they may f l o a t f o r me.ny years Wi8 t h e i r sodden condition causes them to.: sink. It i s n o t unusual
to'
f i n d in t h e tow-net in tins mid-Pacif i c a s o l i t a r y stone, vihioh has bebome so sodden t h a t it h a s not s u f f i c i e n t :buoyancy t o f l o a t i n f r e s h water. , .. .
"The length. of time t h a t pupice w i l l f l o a t i n sea-water is a matter t h a t b e a r s on t h e d i s t r i b u t i o n of t h i s m a t e r i a l over the various oceans. ' J u d g i n g from an experiment I made i n t h e Western P m i f i d , pumice may f l o a t f o r s e v e r a l years before it becomes suff i c i e a t l y sodden.. to s i n k t o the bottom.
I kept f l o a t N g i n seawater f o r two y e a r s a n d 'nine months t h r e e rounded pieces of a n d e s i t i c pumice,' which I o r i g i n a l l y obtained in the tow-net whilse. c r u i s i n g i n t h e Solomon Islands.
Although they had e v i d e n t l y been a long time i n t h e water before
I got them, since they f l o a t e d heavily and had the discolored appeaaance of old drift-pumice, t h e only evident a l t e r a t i o n
in t h e i r buoyancy produced by my experiment was t h a t one piece which f l o a t e d in fresh-water, when I f i r s t obtained it, now sank
. ...
I1The o r i g i n of t h e g r e a t amounts of pumice found on Cocos-Keeling A t o l l was a l s o discussed a t length by Guppy (1889, pp. 284-28618
"I s h e l l r e f e r more t h a n onoe in these papers t o t h e p a r t which t h e pumice derived from t h e great Krakatoa erup- t i o n of 1883 has taken i n reclaiming land from lagoon. hiarrow i n l e t s have been o b l i t e r a t e d and t h e shallow water around t h e lagoon has been in places f i l l e d up by f i e l d s of f l o a t i n g pumice t h a t d r i f t e d inside t h e r e e f s . The Krakatoa pumice, r e a d i l y known by i t s white and f r e s h appearance and i t s un- sodden t e x t u r e , i s t o be found a t present in great q u a n t i t y on t h e beaches
....
but t h e r e i s another kind of t h i s material, apparently elsewhere derived, though of somewhat s i m i l a r com- position, whioh i s found i n s i d e t h e r a i s e d weather margins of the islands, and extends f o r some 20 paces o r more amongst t h e t r e e s . It i s of much g r e a t e r age; and w h i l s t i t s outersurfsce i s darkened by weathering, i t s i n t e r i o r i s often sodden and half-rotten. There i s a l s o a black and heavier pumice, formed of a more b a s i c lava, which i s known ( r i g h t l y o r wrong1;r) amongst t h e r e s i d e n t s a s t h e Tomboro pumice, and
i s found amidst t h e vegetation 15-20 paces in from t h e weather beaches. It v a r i e s in s i z e from a walnut t o a cooo-nut; and, unlike t h e two f e l s p a t h i c kinds of pumice above r e f e r r e d t o , it withskands decay, so t h a t although it has been known i n t h e i s l a n d f o r half a century and more, i t s i n t e r n a l substance
i s s t i l l unaltered
,.. .
'Vherever, in these islands, a l a y e r of old pumice over- l i e s t h e sandy s o i l n e s r t h e beach, an abundance of volcanic minerals, e s p e c i a l l y magnetite, occurs in t h e s o i l . By means
of a magaet, a number of f i n e p a r t i c l e s of magnetite can be c o l l e c t e d from a saucer f i l l e d with t h e white calcareous sand t h a t i s found between t h e tide-marks upon t h e beaches
....
The l o c a l evidence would seem t o show t h a t they p h e grains of magnetite with t h e i r occasicnalLy attached semifused f e l d - spar o r y s t a l s ~ a r e derived from t h e &cay of pumice t h a t i s stranded in such l a r g e q u a n t i t i e s on he se beaches, e s p e c i a l l y since I found them i n g r e a t e s t abundanoe in t h e sandy s o i l underlying an old bed of pumice. Their l a r g e mean size, viz
.,
h a l f a millimetre, and t h e s p e c i f i c g r a v i t y of the mineral, would seem t o favour t h i s opinion. It should, however, be noted t h a t during t h e n i g h t f o l h v i n g t h e great eruption i n t h e Sunda S t r a i t s , some 700 miles away, f i n e pumice dust f e l l over t h e Cocos-Keeling I s l a n d s i n such quantity t h a t on t h e succeeding morning it was found covering the deck of a schooner, t h a t l a y a t anchor i n t h e lagoon, with a l a y e r a quarter of an inch deep
....
I twood-Jones (1910,
in.
170-171) a l s o discussed t h e o r i g i n of the Cocos-Keel+g 'punice :"On t h e seaward beaches i s thrown t h e flotsam and
. . jetsam t h a t reaches t h e group from the outside world,
and one of t h e p r i n c i p a l items,-one t h a t has i n many places oaused a considerable a l t e r a t i o n in t h e character of t h e islands
-
i s pumice. ?he g r e a t e r p a r t of t h e pumice found i n t h e group arrived a f t e r t h e eruption of ICrakatkj being washed up in 1883 in v a s t q u a n t i t i e s . ' ~ k , ~ m i c b , l i g h t e s t of a l l t h e wre.ck t h a t t h e sea has ..p i l e d up, has been c a r r i e d f o r varying distances i n t o t h e island from t h e seaward beach, and shom, a s an index, t h e ' l i m i t of surf a a t i o q i n t h e island building tbt: has been' ree.ched i n %westy t h r e e years. It occurs i n great $u&ti$iep a $ rounded' .&a-worn masses, some
being a f o o t orn;ore in t h e i r long. a x i s , ' b u t the m a j o r i t y . varying from t h e Size, of marbles t o t h a t of c r i c k e t b a l l s . Besides the Ilrakatua pumice,, which l i e s t ~ - d a y mostly on t h e seaward beaches, ar.d f o r a few paces i n t o t h e i s l a n d
i t s e l f , t h e r e i s older pumice which may be found almost anywhere in t h e breadth of the dry land. Pumice has been a r r i v i n g from somewhere ever since t h e f i r s t ap- pearance of land in t h e a t o l l ring, and has, during t h e period of i t s stay, undergone much deooaposition. The Krakatau pumice i s almost uniformly grey, and i s f r e s h
and clears: but pumice e x i s t s f a r from.the sea t h a t has becone impregnated w i t h foreign substances, and i s
in many places e n t i r e l y f r a g e n t e d . The various stages of pumice degeneration may be t r a c e d from the' sea beach t o t h e i n t e r i o r of t h e island. Some of t h e pumice has never been grey, and rounded blocks of a black and
oinder-like substance a r e here and t h e r e found in p a r t s of tfie island where p w i b e has been most f r e e l y washed ashore. . This punice does'not a p p e a r t o belong t o any one p a r t i c u l a r period, f o r , .it is found to-day on t h e beaches, and in t h e i s l a n d s , but i t s composition where- ever found appears t o be t h e same, and, on f r a c t u r e , i t s i n t e r n a l p a r t i s always shining and fresh-looking, i f it be picked up on the beach o r f a r i q t h e c e n t e r of an island."
Wood-Jones, l i k e Guppy, was interested in p l a n t and animal
d i s p e r s a l ar.d devoted a chapter of h i s book t o t h i s and r e l a t e d subjects, In it, he went back t o t h e subject of pumice (pp. 290-291) and said of Krakatau pumice: "This pumice h a s been t o u r i n g the ocean f o r over twenty years, and s t i l l , in t h e Sunda StraLts, some s e t of current w i l l send whole masses t o sea, and a s h i p v ; i l l s t e m f o r h a l f .
an
hour through t h e bob'oing white b a l l s of pumice which a r e launched upon an i n d e f i n i t e , and an irresponsible journey." O f t h e pumice older',:thqn t h a t a t t r i b u t e d t o Krakatau he says: "This i s most probably t h e pumic,e, ~s,et a d r i f t in t h e April of 1615, when the uupara.lleled eruption of Tomboro-
t h e g r e a tvolcano of Smbawa took place." He adds: "The blocks of pumice s e t a d r i f t by the eruptions have been navigating t h e Eastern seas ever since . . . . I '
V i s i t o r s t o Diego Garcia, Chagos Archipelago, were undoubtedly c o r r e c t in b e l i e v i n g t h e pumice t h e y observed t o be a product of t h e 1883 e r u p t i o n : ' by a happy coincideaoe, t n o n a . t u r a l i s t s , F i n s c h and Wilson,
stopped a t Diego Garcia ( t h e n a c o a l i n g s t a t i o n ) in 1884 and published t h e i r o b s e r v a t i o n s on t h e a t o l l . F'iusch, (1887, p. 42) observed pumice on t h e lagoon s t r a n d and on t h e o u t e r shore "in g r e a t qu.cntity." Later, h i s s h i p encountered g r e a t d r i f t i n g masses of pumice a t sea. R. F. M.
Wilson (1889, p. 144) s p e n t o n l y a n hour on t h e a t o l l and mentions l a r g e q u a n t i t i e s of pumice: "There must be t o n s of it l y i n g on t h i s beach." A t sea, he a l s o observed it, but i n "wrea"Y:ls." The Nautical Magazine in t h e l a s t months of 1883 r e p e a t e d l y warned i t s read.ers of t h e
changes in t h e Sunda S t r a i t and s a i d (p. 852): "In some p a r t s of t h e S t r a i t s t h e pumice s t o n e i s 7 f t . t o 8 f t , deep."
Another i n s t a n c e in wnich t h e source of pumice vias r i g h t l y i d e n t i f i e d a s Krakatau i s r e p o r t e d from Ramesvraram I s l a n d , a t t h e n o r t h - west end of "Adam's Bridge" i n t h e Gulf of Marmar, between I n d i a and Ceylon, by Foote (1889, p. 835):
"As vre walked eastward a l o n g t h e beach our a t t e n t i o n vias a t t r a c t e d h e r e and t h e r e by tine q u a n t i t y of pumice s t o n e
thrown up. Not a v e s t i g e of pumice was seen a l o n g t h e beach when I v i s i t e d it i n 1882, but now it abounded, having been d r i f t a d from t h e s t r a i t s of Sunda a f t e r t h e t e r r i b l e e r u p t i o n of Krakatao i n 1883. The pumice fragments were of a l l s i z e s , from a p i n ' s head up t o a c i i i l d ' s head, and most of them showed s i g n s of t h e i r l o n g s e a voyage, in t h e form of in- c r u s t a t i o n s of n u l l i p o r e s of s e r p u l a e o r of f l u s t r a e and o t h e r e q u a l l y l o v e l y polyzoa, t o g e t h e r w i t h s e r p u l a e of s e v e r a l s p e c i e s . Many specimens showed a l s o adherent young v a l v e s of a v e r y p r e t t y white and crimson s p e c i e s of Spondylus. It was impossible n o t t o be s t r u c k b y t h e g r e a t =bar of z o o l o g i c a l , geographical, and
g e o l o g i c a l f a c t s recorded by t h e s e i n t e r e s t i n g specimens. I t O f t h e pumice observed i n t h e Maldives and Laccadives d u r i n g
h i s e x p e d i t i o n Gardiner (1906, p. 582) says: "On t h e s h o r e s of many of t h e i s l a n d s t h e r e a r e l i n e s of pumice, which t h e n a t i v e s s t a t e were washed up a b o u t 1885, and woula hence have probably owed t h e i r o r i g i n t o t h e erup- t i o n of Krakatoa in 1883. I n a d d i t i o n half-decomposed p m i c e i s fouad?
i n p l a c e s a t some c o n s i d e r a b l e d i s t a n c e inland, which e v i d e n t l y belonged t o an e a r l i e r period." E l l i s (1924, p. 9 ) in an account of t h e Laccadives, q u o t e s Gardinerts suggestion t h a k pumice found in t h e Maldives came from Krakatau, and adds t h a t in t h e Laccadives, l a r g e beds of pumice were r e -
p o r t e d a f t e r 1883, "which have nav e n t i r e l y disappeared. Only s c a t t e r e d p i e c e s much water-worn a r e now found." Sewell (1956 a, p. 77) a l s o at- t r i b u t e d t h e o r i g i n of t h e pumice observed on t h e Maldives t o t h e e r u p t i o n of Krakatau i n 1883 (see p. 4 of t h i s paper).
The 1883 e r u p t i o n , however, d e s p i t e i t s v i o l e n c e and t h e s e n s a t i o n it caused, was n o t t h e only source of puraice found in t h e I n d i a n Ocean:
Moresby (1844, p. 309) found pumice in t h e Chagos I s l a n d s when he surveyed t h e a r c h i p e l a g o in 1836-37.
. . . ... . . . -10-
. . . , . . .
g o s t a W i o r s quoted here a t t r i b u t e tb.e o r i g i n of the pumice d i r e o t - l y t o volcanic e r u p t , i y s . T h i s is u n d ~ u b t e d l y ~ t h e uoua: oase, but it seems coiiceiviblei t h k t idme of t h i s mat+&ci..m'ight be launched onto t h e sea by t h e ' a c t i o n of 't&i k a m s underc@tip&'t.hee. slopes. o f some of t h e numerous oolbanic oo&s found in t h e - P a ~ S f i i q : ~ . ; , ~ ~ o r n ~ of thi,s bobbing pumice may w e l l have spent s'gcbd p a r t OP its','ik&.!.as p a r t of a';-&lceso's d o p e ,
before being f r e e d and s e t . a d r g t in the' cone's erosion. ' . '.
~. . . ' ... ..,.
Lacroi:: (1939:ti, p..'610) disct+3sing t h e pumice :&lected by Seurat in South IVla?utes. (l'uatb'cus) relllarked that t h i s chemical.-mkeralogia type . ' of rook was known i n t h e South P a c i f i c o n l y from Easter and Tu'cuila I s l a n d s and suggested an ori.gin f o r it i n a hy<othetical submar'i8e voloano t h a t might have e x i s % e d . i n sorue p a r t of t h i s vast region, I t i s not c l e a r
whether he had in mint an underwater e r u p t i o n o r a cone t h a t extended above ' ' t h e surface and was ;subsequently o u t away by t h e waves, but he probably . - . meant t h e l a t t e r . I n ' m y e ~ ~ e n t , it does n o t seen necessary t o p o s t u l a t e
t h e existenoe of such a volcano, because it is q u i t e possible ' f o r pumice , , t o f l o a t from Easter I s l a n d o r elsewhere t o S. bU8rxbea.
The p o s s i b i l i t y should n o t
be
overlooked t h a t some of t h i s material, f o r e x w p l e t h e coarse, blac!rvslriety found by Fosbergh
the ~!larshalls., might- n.ot b$ pumice a t a l l b u t c l i n k e r s . from t h e furnaces of coal-burnirig . .shipso Su.ch have beon reportsd. c a i t 'hp'on .the. '&or& of Lake y&c&gan by' D r . Helen Poster and
Xu.
Gilbert Corwiri (conversation.$, 1.954), This may be determined f o r t h e i"~a.rshali I s l a n d s m a t e r i a l by' f u t u r e p e t r o l o g i c a l s t u d i e s ,. . . . . . . . . . . . . . . . !: . .
. .
. ,
Chemical a$ & t r o l o g i c 8 1 nat$" .: ..:
. . . . . .
.... . . . : . . .
... . . . . ..: . . .
~n ' obstacle t o . th e di.scussion of t h e oyi&n o f $ec.es, of pumice found on a t ~ l & ~ , . i & t h e : f a e t . t h a t . feW.ha.ve e v e r been s t u d i e d f o r t h e i r
p e t r o l o g i c a l ch&a$ter and clio.'Rical. compos.ition. , ~ e c e n t
'unpublished
analyses of such m a t e r i a l , ~ . i - L l . be found i n an addendum t o t h i s ' p a p e r , p. 21,C . , .
'
. Lacroix. based h i s remarks
(1939a).
on s e v e ~ a l :analyses -includirig, ' one -by ,r($oult. of S o u t h Ma1:utea ~ ~ t e r i a l , (Lacroix
L928,
pp.44-45.
This.' i s as f o i 1 . o ~ ~ :, . '
. . . .
- MgO
. . . CaO
l$a;Q, K2°
Ti02 '2'5
. .
. , . ..., Percent
, .,
...
. . .....
...1
69.40Percent
Hz0 (+) ...as..
- 1.57
Lacroix described t h i s m a t e r i a l ag a r h y o l i t h i c pumice, "formed of
volcanic g l a s s with elongated c a v i t i e s , which contain a few hexagonal p l a t e s of b i o t i t e " a s the only c r y s t a l i z e d minarals. He remarked t h a t i t s chemical composition showed in any case t h a t it could not be pumice from Krakatau.
He pointed out a s i m i l a r i t y with t h e t r a c h y t e from nearby P i t c a i r n Island, suggesting t h a t t h e pumice might not have came from too f a r away.
The pumice from Funafuti was examined by Cooksey (1896, p. 77):
"Pumice Pebbles.
- --- --
Pebbles of pumice stone, t h e l a r g e s t of which resemble a walnut in size, a l l much water worn and rounded, were collected from various places on t h e outer c i r - cumference of t h e Atoll, and possibly occur on a l l of t h e s e i s l e t s . They possess a f i b r o u s t e x t u r e , and oontain macro- scopic c r y s t a l s of sanidine. The colour v a r i e s from l i g h t t o dark grey, one o r two having a b r o m o r greenish tinge."An a n a l y s i s of one which was much rounded by a t t r i t i o n , and possasse'd a very l i g h t grey colour, gave t h e following percentage composition:--
Eiygroscopic moisture
...
Loss on i g n i t i o n
...
Si02
...
...
Fe203
...
A1203
CaO . .
...
%O .
...
.
*20 ,
...
Na20
... ...
'2'3 . , . .
...
,
t r a c e 100.96
"A p a r t i a l a n a l y s i s of another pebble of a darker shade
gave 60.37% of SiOZ."
Cooksey noted t h a t t h e f i g u r e s i n t h i s a n a l y s i s agreed very c l o s e l y with r e s u l t s of analyses of material from t h e 1883 Krakatau eruption but thought
-12- ... ' ,
t h i s volcano too f a r away t o be .a.,.likely source of t h e pumice in Funafuti.
--., ,
-
. ..
, .
.:
. ~,.:i .I
In t h e Gilbert Islands t h e U. S. i&~:jchl'ork,~ E x p e d i t i o n l e a r n e d t h a t pumice was gathered by t h e i n h a b i t t q t s and pounded up t o f e r t i l i z e t h e s o i l of the: t a r o p i t s ; in, addition, Wilkes (1849; .vd. .5: p. 81) writes: "the coconut t r e e s are., &qced round;. aa&-pounded, pumice i s mixed :with t h e s o i l near t h e i ? soots'.' :.T.h,is stone 'Ys' o d l 1 ~ c t e . d
by
t h e women, who, a r e frequently t o be seen i n n m b r s . - o ~ , t . h e ~ b ~ a c l i e s , . . , . : : . aftelf westerly winds, 'picking 'it up,. . ,
in small baskets.'' . .; . . , . .
:.
. . , ... ,
Ha?tz,er, a m i s s i ~ n b . i - ~ (1900, p. 4 3 ) w r i t e s in a l m o s t t h e same words,:,.
and so does 'Xuafie .(..1887, , p l , 68). Such observations. on the t a r o - p i t s have . , ' "
been made o r quoted by others; 'such a s hTe.inicke (1863, p. 405) and Finsch . . '
(1893, p. 52). Gulick ( 1 8 6 2 , ~ . 413) a l ' s o described t h e c a r e f u l tending of t h e t a r o - p i t s but sald'that''!sbi& was. brought t o them in basli'&Ws and 1 s h i f t e d . He d i d s o t mention p b i c : e . . Probably both were ,@ded t o t h e '.., various leaves, which were shredded and thrown i n t o t h e 'pit&;:.. A s i m i l a r
instance i s found in Grundemaiin (1887, p. 442)s ~ c c o r d i n g , t o ' h f m ; on Ailuk in t h e Marshalls, s o i l and leaves were thrown i n t o t h e ' p i t . s , a n d pumice, when available, was ground up and added. This i s t h e oli1.y reoord of t h i s p r a c t i c e i n t h e Marshall Islands. S i m i l a r l y Cloud's observation of t h e use of pumice a s f e r t i l i z e r on Kayangel A t o l l , Palau (personal conununication, L953), i s t h e only record f o r t h e Caroline Islands.
I n s p i t e of i t s abundance on t h e E l l i c e Islands, pumioe does n o t seem t o have been used t h e r e a s in t h e Gilberts. I t might be pointed out here t h a t the Gilbert Islands a r e t h e most densely populated of a l l a t o l l s and a t the same time one of t h e driest'.&$ most s t e r i l e of t h e inhabited a t o l l s and a t the same time one of the d r i e s t and most s t e r i l e of t h e in- habited a t o l l groups. I n t h i s connec<ion it i s noteworthy t h a t pumioe i s
used a s f e r t i l i z e r in another densely populated group, t h e Maldive Islands.
Gardiner (Willis and Gardiner, 1901, p. 121.) says t h a t on Suvadiva, p l a n t a i n s a r e grown in p i t s dug t o below high t i d e l e v e l "and on Kondai [islet of
~ u v a d i v a J I saw a man put in a basket a p w i c e from t h e beach; t h i s ap- peared on enquiry t o be a regular custom of t h e island."
. .
I n a d d i t i o n t o i t s r o l e in a t o l l a g r i c u l t u r e , pumice i s often used on these limestone islands a s an abrasive, I n t h e Gilberts, Finsch (1914, p. 254) says t h a t pumioe was used t o . p o l i s h and smooth wood, s h e l l , and c o r a l . In Ujae (Fosberg, unpublished obbervations 1951-52), t h e iblarshallese c a l l e d it by t h e name " t i l a n , " and ,they s a i d they used it l i k e sandpaper.
A l a r g e piece of a black, coarse-grained, hard v a r i e t y was seen in use a s a whetstone f o r machetes on Bock I s l e t , Ujae.
. . .
Ecological significance
Very l i t t l e f a o t u a l information is a v a i l a b l e on t h e ecological significanoe of pumice on a t o l l s . Several authors have discussed it, following t h r e e main l i n e s of speoulation: One i s t h e p o s s i b l e r o l e of pumioe i n t h e dissemination of animals from one shore t o another. Another
i s the information . t h a t puniide-has been supposed t o f u r n i s h on ancient shore- l i n e s . The most important~is'the.:possible. influence of pumioe on t h e growth
a
.
of plants..
. . .
Some of ,the, above-mentioned authors, such as; p i t m e e and Guppy, have sp.oken df 'plebes -of $&ibeincrusted with marine kfiimal's 'such a s annelids, ,pirripeds,,,biva&yes. Wood-Jones (1910,. p.. 291), a f t e r h i s dis- cussion of .the d r i g i n of s t r a n d e d pumice (see p. 8 of: t h i s ?aper) added:
"the blocks o f ' $ m i c e
..,.
have ' v i s i t e d many shores in t h e course, of t h e i r t r a v e l s , an8 have o.oribt,ituted a m i g h t y f l e e t of passenger. v e s s e l s f o r t h e use of Xaturefs colonists." I n 'some cases pumicemajr p l a y a c e r t a i n r o l ein t h e dissemination of marine forms, but it seems t h a t Wood-Jones ex- aggerated t h e "mightiness" of t h e e f f e c t .
~ i i ~ p ~ f s chapter on p,umic$' d r i f t (i887;
,?p.
137-144). in s p i t e of some' h a s t y and r e g r e t t a b l e a s s e r t i o p (a; footnote on p. 143 says t h a t"the t r e e s of the' center of a c o r a l 2sltit ,gr.oW from seeds e j e c t e d by. t h e fruit-Pigeons),. contains a wealth o f f a a t s , &d 'is one of t h e few com- p i l a t i o n s and discussions of t h e i n t r i g & T g @ o b l e r n of stranded pumice.
The author attem$s t o c l k r i f y
%hi
ecologio& significance of t h i s m a t e r i a l . Unfortunately he had a tendenoy, a t time a , , t o l e t h i s keen observatibns . .be colored by t h e t h e o r i e s dear to. him. ' Thus,' . . . h i s n 6 t e s on t h e d i s - ' , . ...
. . t r i b u t i o n of purnioe hebbles on i s l e t s (Guppy, 1 8 8 7 , p . 1 4 l ) , he mix6s
f a c t s and assumptions:.' . . . ,
. . .
. . .
. . . "I s h a l l s u b ~ & ~ u ~ n t l ~ point
kt,
Chat a s *e oross a ' coral i s l e t from i t s vieather or newer portion, the' p m i c e pebbles.'become fewer pad more decayed, u n t i l they f i n a l l y disappear i n t h e leeward o r oxder p a r t of the i s l e t . , Sucha f a c t proves t h a t t h i s . m a t e r i a 1 , has n o t been swepk over . the' surface of t& i s l e t by a wave, such a s t h o s e ' . . .
which follow ear-bhquakes, but t h a t , whilst t h e i s l e t has . .
. / been growing sea-ward w i t h . .: .. t h e reef i n t h e course of ages, -
. . . .
p;mih'e '.has a t widely:: d i f f e r e n t times been stranded on i t s . ... . shocis; The 'd&a:~ed: pw&ce pebble, t h a t n&f l i e s among . . . .
: . . . . . .
. . the'&-e& i n t h e 'lt&erioi- of t h e i s l e t , remains where t h e . . , ...
: ,eb%in'n'g-tide leYX it long ago. The same explanation i s a l s o ' .
,
.... ... ,:. applica%le t o t h e $mice pebbles found on c o r a l i s l e t s and r e e f s t h a t have experienoed s ~ m e d e g r e e of elevation.
Doubtless t h e "'gre'at s e a ' WE&" pr,@uce'd, by an earthquake h a s somet'imes di&rihuted t h e p~:;io,$,;pebbles ly i n g on t h e
beach, over t h e surfa&i
$f
t h e ,isleti;: p*t'''if it w i l l . b$ found,.:a s ' I believe, ' t o - b e &n&$ally: tr.ue;' t h a t . the pebbles gf$
fewer and more decayed a's we pro&$
h t o
t h e i n t e r i o r , wes must look t o some other.agendy2%hair . . . t h a t of t h e . "great sea , ' . . .
;
' . - ,wave." In some o o r a l i s l a n d s ~ ~ h i b h ' a r e plaoed i n u n p r o t e c t - , ,
. . . .
ed p o s i t i o n s i n t h e P a c i f i c , p,$ice p e y ~ l e s a r e found only : . . . .
in the i n t e r i o r and n o t on. thti; beaoh. It would' seem mos.V probable t h a i ' t h e force o f t h e v r i d 'during s t o m s w o u l ~ be s u f f i & n t t o sweep t h e l i g h t piin$be"pebbles off the-beach and 'moi?&t :%hi: bordering vegetation.
. . . ..
. .
. " A l l 'the' 'evidence $ 6 e s t o show t h a t .in a compar&tively dry climate and on porous s o i l itranditd '$miice i k y r e s l ' s t f o r ages t h e d i s i n t e g r a t i n g e f f eotg of t h e atmosp$eric agencies."
. . . . . .
.. ..
: : . . . . . . . . . ,.., ..
.,..
.. ~ u p p y &&s ori t o describe t h e distribt&ioi;'6f 'the pebble.s'oq
:
c o r a l i s l e t s i n t h e Solomons and shows them t o b e fewer and.more debom-
posed toward t h e i n t e r i o r , disappearing eventually on t h e l e e side.
'i . '
"Those obtained within 20 or 30. paces from t h e beach . , . . . f l o a t e d buoyantly in the sea, but out o f those found a t . .
. . :I:
. . d i s t a n c e s g r e a t e r then 100 ywds, more than half sank. The' , .
pumice pebbles f u r t h e s t from t h e beach werq: evidently of . . . ' ' . ' .
g r e a t e r age and had been exposed f o r a longer time t o t h e .
wet." . . . .
No doubt, on c e r t a i n islarids
--
possibly on some of t h o s e , e x m i n e d by Guppy--
older pumice brought by one of t h e ; v a r i o u s l y cause& . . "great . . waves'', which may a t . tjmes comple.i;ely oover low. c o r a l i s l e t s , ' i s ' S a r t l yremoved from t h e beaohes by subsequent l e s s e r storms and l a t e r happens t o be.surrounded by younger pumice, l e f t stranded in windrows by t h e , ordinary. t i d e w (See quotation of Gardiner on p. 9 of t h i s paper). This does n o t n e c e s s a r i l y meen t h a t t h e i s l e t has beeome l a r g e r , o f f e r i n g more space f o r new pumice.. The contours and t o t a l a r e a of i s l e t s do change of 'course, and i f an islet'bscame l a r g e r , it might b e f r o m i t s seaward side,
but t h e aspect and d i s t r i b u 6 i d n of p m i c e a r e not s u f f i c i e n t t o permit a reconstruction of t h e change. However, i n c e r t a i n special l o c a t i o n s and when other
evJ&n5.e g
a v a i l a b i 3 pumice pebbles arranged i n l i n e s , w e l l inland, may i n d i c a t e a change ul shore&,$ne. ..Stode (1951, p, 2).w r i t i n g of Aiino A t o l l , ~ & r s h a l l Islands, says "The.. progressive widening of krno Island, although now slow, i s known t o the.pBople t h e r e because inland and 2 a r a l l e l with t h e beach t h e y f i n d rows of pumice pebbles, such a s occur along t h e present beach." (See a l s o quotation of ~ e w e l l o n p. 1 8
.., ...
of t h i s paper). . .
...
That Guppy does &t r$al.iie t h e t r u e r e l a t i o n s h i p betikeei topo- graphy of an i s l e t , s o i l ' a n d vegetation i s vrell shown in. h i s next t o p i c : He assumes (Guppy, 1887, p.
143).
t h a t s o i l g e t s t h i c k e r and r i c h e r from seaward t o l e e s i d e o f a n i s l & because "we pass. . .
from i t s newest. t o i t s o l d e s t portion" a n d ' t i e r e f o r a p y h e has had more time t o form s o i l , has been completely deco~nposed,:and indeed, c a n n o t b e foundanymore on t h e l e e sibe. Actually t h e r e G a y u e % r 'have been a s muoh puIuice in the:center and on t h e l e e side of t h i s ' i s i e t 'as on t h e seaward sidei.-:Vegetation does change a s one goes from seawkira t o t h e more protected sid&;bf t h e i s l e t , but t h i s change i s brought about by t h e topography and $tr'ucture of t h e i s l e t and the diminution b't& e f f e c t s of wave, wind, spray, i t c . The vegetation in t u r n , t o g e t h e r X w i t h these same f a c t o r s , determines t h e vari- a t i o n in t h e abundance of s o i l , which i s indeed:often t h i e k e r in t h ecenter, o r toward t h e l e e side of an island, o r t h e lagoon s i d e of an a t o l l i . s l e t . But t h i s zonation of s o i l and vegetation i s q u i t e inde- pendent of t h e presence of pumice. It i s possible, of cjoursq, t h a t given a uniform pumice l a y e r over an i s l e t t o begin with, the'.~?pi&iee might de- compose somewhat f a s t e r near the c e n t e r of t h e i s l e t than on 'the sealyard side, because a t h i c k e r and f a s t e r formifig s o i l and humus i a y b in t h i s center would provide a greater abundance of t h e substances t h a t cause t h e
decompos it ion of t h e pumice pebbles. . . . .
While Guppy t r i e d t o prove t h e b e n e f i c i a l influence of p i i o e ' Gn the vegetation of a c o r a l i s l e t , other authors took it q u i t e f o r granted.
Scherzer (1862, p. 607) says:
"Another geological p e c u l i a r i t y i s t h e ocourrence of heaps of pumice-stone. These a r e found arbout t h e s i z e of walnuts over t h e e n t i r e i n t e r i o r of paole- a t those p l a c e s vrhich t @ e swell b f the-wavescannot reach even in t h a storn-
i e s t weather, where they ocour in such immense' q u a n t i t i e s (though thore. a r e no t r a c e s ~f them on t h e sand o r shingle of t h e a c t u a l beach):that we may take f o r granted t h a t t h e convulsion which brought t h e n here mst have occurred in times, long gone by, t h e more. so a s t h i s s u p e r p o s e d pumico- stone e x e r c i s e s a marked and obvious influence. upon t h e vegetation of t h e island. So f a r a s i t s . s o i l c o n s i s t s of heaps of fragnlents of coral and mussel-shells, the cocoa- n u t palm reigns alinost alone, where8.s a s soon a s t h e pumice-
stone region i s readked, t h e r e begins an exceedingly luxur- i a n t growth of l o f t y f o ~ e s t t r e e s with huge trunks and umbrageous f o l i a g e , and a? astonishing abundant f l o r a of species a p ~ a r e n t l y peculiar t o these A t o l l ~ s l a n p
This c o r r e l a t i o n of vegotafion with substratum, a l s o nentioned ' .
by Hcohstetter, may be sov.ewf:at i l l u s o r y , since t h e coconut palms were probably planted by t h e na-tives i n a r i n g around t h e i s l e t , and , t h e luxur-
iance of t h e mixed f o r e s t , which includes b r e a d f r u i t t r e e s , i s hot t o o unusual i n a vqry v e t a t o l l such a s Sikaiana. Yet t h e observations by Scherzer ahd' Hochstetter a r e ' v e r y i n t e r e s t i n g . I t w o u l d c e r t a i n l y be worth~vhile t o f i n d ,out now, alinost 200 years l a t e r , what t h e s o i l of Faule I s l e % i s l i k e and whether any t r a c e s remain of t h e abundant pumice l a y e r observed by t h e n a t u r a l i s t s of t h e "Novara."
Other nonoalcareous rooks
. .
iTaricus extraneous m a t e r i a l s o t h e r . than pumice a r e found on a t o l l s : these a r e various stones, muds, e t c . , found among t h e r o o t s of d r i f t t r e e s , o r supposedly brought by them, other pieces of rock o r even masses of coal o r s o i l imported by men f o r various. reasons, and f i n a l l y t h e mysterious
"basalt blocks" described from various i s l a n b . . .
The l a t t e r a r e of special i n t e r e s t on Rose A t o l l , American Samoa. This very small, uninhabited, a n d i s o l a t e d island may ha& been f i r s t 1.anded.on by members of t h e U. S. Exploring Expedition (1838-42).
Dana (1849, pp. 77-78) says t h a t t h e o f f i c e r s on t h e Vincennes observed blocks of oodpact c e l l u l a r b a s a l t on Rdse, l y i n g 2C0 yards inside t h e l i n e of breakers. Wilkes (1845, 'vol. 2, p. 64) s d a s t h a t "they were - . from twenty t o t w o hundred pounds m i g h t , and were found among blocks of c o r a l coiiglomerate." Unfortunately, Dana h h s e l f d i d n o t land on Rose, being on another s h i p . Couthouy (1842, p. 138),. who was prob,ably. thefe, . .
says t h a t t h e voloanio boulders were found on t h e sandy lagoon bottom : and were siniilar 'in appearance and mineral s t r u c t u r e t o t h e rooks forming t h e mass of Samoa and T a h i t i and that one of 'them wsighing about 20 pounds was picked up i n 4 f e e t of water k o n g small r o l l e d blook's of coraloon-.
glomerate
.
. A t l e a s t one member of the landing part.y of t h e " ~ i n c s n n e s " . . ; published h i s own account of t h e discovery, a1thoue;hhis book i s not p a r t of t h e o f f i c i a l e d i t i o n of t h e Expedition r e s u l t s ; Pickering (1876, p. 235) w r i t e s :. . . . . , . .. .
