2. geology and geomorphology of little cayman

2 . GEOLOGY AND GEOMORPHOLOGY OF LITTLE CAYMAN

D.R. S t o d d a r t

I n t r o d u c t i o n

L i t t l e Cayman forms one o f t h e emergent i s l a n d s a l o n g t h e n o r t h e r n r i m o f t h e Cayman Trench, between t h e S i e r r a Maestra o f Cuba and t h e Gulf o f Honduras. The Trench i t s e l f i s 1700 km l o n g and more t h a n 100 km wide (Uchupi 1 9 7 5 ) . I t i n c l u d e s t h e O r i e n t e , B a r t l e t t and M i s t e r i o s a Deeps, a l l r e a c h i n g more t h a n 6000 m d e p t h . The n e a r e s t l a n d a r e a s t o t h e Cayman I s l a n d s ( o t h e r t h a n C u b a ) , such a s Jamaica and t h e Swan I s l a n d s , l i e on t h e s o u t h e r n s i d e o f t h e Trench.

E a r l y workers such a s Taber (1922) c o n s i d e r e d t h e Trench t o be t h e s i t e o f massive l a t e r a l movement. Such views have had t o b e modified i n t h e l i g h t o f p l a t e t e c t o n i c t h e o r y , though some workers s t i l l e n v i s a g e l a t e r a l movement a l o n g i t of up t o 1000 km. I t i s known t h a t

g r a n o d i o r i t e s o u t c r o p i n t h e w a l l s o f t h e Trench a t d e p t h s o f 600- 3400 m , and g e o p h y s i c a l d a t a s u g g e s t a p o s s i b l e t e n s i o n a l o r i g i n . S p r e a d i n g r a t e s have been i n f e r r e d o f 0 . 4 cm/year s i n c e t h e Eocene, a c c o u n t i n g f o r 2 0 0 km o f l e f t - l a t e r a l d i s p l a c e m e n t between t h e Cayman Ridge and t h e Nicaraguan P l a t e a u ( P e r f i t and Heezen 1 9 7 8 ) ; o t h e r

workers s u g g e s t g r e a t e r r a t e s of s p r e a d i n g (Macdonald and Holcombe 1 9 7 8 ) . The Cayman I s l a n d s t h e m s e l v e s p r o b a b l y have a g r a n o d i o r i t e f o u n d a t i o n , capped b y b a s a l t , and o v e r l a i n by m i d - T e r t i a r y and l a t e r c a r b o n a t e s . P e r f i t and Heezen (1978) s u g g e s t a g e n e r a l s u b s i d e n c e r a t e o f 6 cm/1000 y e a r s d u r i n g t h e c a r b o n a t e a c c u m u l a t i o n , b u t t h e exposure o f marine l i m e s t o n e s i n each of t h e Cayman I s l a n d s i n d i c a t e s l o c a l u p l i f t .

Unpublished work on t h e l a t e Q u a t e r n a r y s h o r e l i n e s o f a l l t h r e e Cayman I s l a n d s (Woodroffe and S t o d d a r t , i n litt.) i n d i c a t e s t h a t Grand Cayman, Cayman Brac and L i t t l e Cayman have e a c h moved i n d e p e n d e n t l y w i t h r e s p e c t t o s e a - l e v e l o v e r t h e l a s t 100,000 y e a r s .

A t o l l Research B u l l e t i n No. 2 4 1 : 11-16, 1980

Rock u n i t s and landforms

Matley (1926) d e f i n e d two main l i t h o l o g i c u n i t s i n t h e Cayman I s l a n d s : t h e B l u f f Limestone o f m i d - T e r t i a r y age and t h e I r o n s h o r e

Formation of P l e i s t o c e n e a g e . Matley v i s i t e d L i t t l e Cayman and produced a s m a l l - s c a l e g e o l o g i c a l s k e t c h map, i n d i c a t i n g t h a t t h e e a s t e r n h a l f of t h e i s l a n d c o n s i s t e d of B l u f f Limestone, w i t h a narrow p e r i p h e r a l b e l t of I r o n s h o r e , and t h e w e s t e r n h a l f c o n s i s t e d e n t i r e l y of I r o n s h o r e . A s h e d e s c r i b e d i t , t h e B l u f f Limestone formed a " h i g h l y honeycombed l i m e s t o n e c o r r o d e d i n t o jagged n e e d l e s o f rock and c o v e r e d w i t h i r r e g u l a r h o l e s , s i n k - h o l e s and f i s s u r e s " , and c o n s i s t e d o f " h a r d w h i t e

r e c r y s t a l l i s e d l i m e s t o n e " , p r o b a b l y o f Miocene age (Matley 1926, 363- 3 6 5 ) . I t was i n f e r r e d t h a t t h e B l u f f Limestone r e a c h e d a maximum h e i g h t o f 45 f t (14 m) a t Weary H i l l . The I r o n s h o r e Formation i n t h e w e s t c o n s i s t e d o f a lower r e e f f a c i e s o v e r l a i n by bedded l i m e s t o n e r e a c h i n g 10-12 f t (3-3.7 m ) above s e a l e v e l . The boundary between t h e B l u f f Limestone and t h e I r o n s h o r e Formation on M a t l e y ' s map was,

t e n t a t i v e .

No f u r t h e r g e o l o g i c a l o b s e r v a t i o n s were made on L i t t l e Cayman u n t i l t h o s e of Mather ( 1 9 7 1 ) . He t o o d i s t i - n g u i s h e d t h e B l u f f Limestone and t h e I r o n s h o r e Formation. He d e s c r i b e d t h e B l u f f Limestone r e a c h i n g a g e n e r a l maximum h e i g h t o f 20 f t ( 6 m ) , w i t h a p e r i p h e r a l r i d g e

r e a c h i n g 40 f t ( 1 2 m ) i n p l a c e s . The d i - s t r i b u t i o n o f B l u f f Limestone a s mapped by B r u n t et d l . (1973, 2 1 2 ) resembled t h a t shown by Matley.

The I r o n s h o r e Formation was s t u d i e d i n g r e a t e s t d e t a i l by s r u n t et a l , on Grand Cayman, where i t was d i f f e r e n t i a t e d i n t o r e e f , b a c k - r e e f ,

l a g o o n a l , s h o a l , and b e a c h - r i d g e f a c i e s . I n t h e i r t r e a t m e n t o f L i t t l e Cayman, r e e f and b a c k - r e e f f a c i e s were n o t s p e c i f i c a l l y mentioned, b u t it was n o t e d t h a t l a g o o n a l f a c i e s were o f l i m i t e d e x t e n t . They a l s o i d e n t i f i e d " a t a number o f l o c a l i t i e s on

...

L i t t l e Cayman r i d g e s o f c a l c a r e n i t e a t t a i n i n g e l e v a t i o n s of o v e r 7 m above s e a l e v e l " , and commented t h a t " t h e s e r o c k s g e n e r a l l y o v e r l i e s e d i m e n t s of l a g o o n a l f a c i e s " ( B r u n t et al. 1973, 2141, On Grand Cayman s i m i l a r r i d g e s c o n s i s t o f cross-bedded c o l i t e s and a r e i n t e r p r e t e d a s submarine sand r i d g e s formed i n a l a g o o n a l environment. Some o f t h e s e r i d g e s a r e shown di.agrammatically i n a g e o l o g i c a l s k e t c h map o f L i t t l e Cayman

( B r u n t et al. 1973, 212)

.

Nei-ther Matley n o r B r u n t et al. a p p a r e n t l y had much o p p o r t u n i k y t o t r a v e r s e t h e i s l a n d , o r t o r e l a t e t h e c h a r a c t e r i s t i c s o f r o c k s a t

o u t c r o p t o t o p o g r a p h i c f e a t u r e s . More d e t a i l e d s t u d y h a s been made p o s s i b l e by t h e p u b l i c a t i o n of t h e D i r e c t o r a t e of Overseas S u r v e y s

(D.O.S.) t o p o g r a p h i c map a t 1 : 2 5 , 0 0 0 , b a s e d on photogrammetry, w i t h c o n t o u r s a t 20 f t ( 6 m) i n t e r v a l s and some v e g e t a t i o n i n t e r p r e t a t i o n by t h e i n s t a l l a t i o n of a s e r i e s o f c o a s t a l benchmarks by D.O.S., most o f which c o u l d be r e l o c a t e d i n 1975; b y t h e c u t t i n g of a network o f t r a n s - i s l a n d t r a c e s by t h e C a d a s t r a l Survey of t h e Cayman I s l a n d s , mainly d u r i n g 1974; and by t h e m o b i l i t y made p o s s i b l e by t h e c o n s t r u c t i o n o f a r o a d round much of t h e c o a s t i n 1973. A e r i a l p h o t o g r a p h s a r e a l s o a v a i l a b l e a t a s c a l e o f 1 : 1 2 , 5 0 0 , though t h e s e were flown i n 1958 b e f o r e t h e c a d a s t r a l t r a c e s were c u t .

The 1 : 2 5 , 0 0 0 t o p o g r a p h i c map c l e a r l y d e l i n e a t e s a d i s c o n t i n u o u s s e r i e s o f narrow r i d g e s ( F i g u r e 3; P l a t e s 2-4) round t h e p e r i p h e r y o f t h e i s l a n d , immediately i n s h o r e o f t h e c o a s t a l ponds and s a l t f l a t s ; t h e y a r e d e f i n e d by t h e 20 f t ( 6 m ) c o n t o u r , and i s o l a t e d s m a l l s e c t i o n s r e a c h 40 f t (12 m)

.

Using t h i s map and t h e a e r i a l p h o t o g r a p h s an

a t t e m p t was made s o f a r a s p o s s i b l e t o d e f i n e t h e r e l a t i v e e x t e n t o f t h e f o r m a t i o n s d e s c r i b e d b y Matley and B r u n t e t ^dl. Where p o s s i b l e

i n s t r u m e n t a l s u r v e y s were c a r r i e d i n l a n d from t h e c o a s t t o e s t a b l i s h e l e v a t i o n s w i t h r e s p e c t t o s e a l e v e l . F i g u r e 4 shows t h e main

t r a v e r s e s made: i t i s c l e a r t h a t l a r g e a r e a s o f t h e i n t e r i o r were n o t v i s i t e d d i r e c t l y , and t h e a e r i a l p h o t o g r a p h s were used t o e x t r a p o l a t e between t r a v e r s e s .

Two main f e a t u r e s were mapped d u r i n g t h e t r a v e r s e s . The B l u f f Limestone was r e c o g n i s e d ( a ) by i t s h i g h l y d i s s e c t e d s u r f a c e topography, w i t h p i t s , p i n n a c l e s , d e e p h o l e s , and o c c a s i o n a l c o l l a p s e d o l i n e s l e a d i n g

i n t o c a v e s ( P l a t e s 5 - 8 ) , and ( b ) by i t s appearance i n hand specimen a s a d e n s e , w h i t e , e x t r e m e l y h a r d , l a r g e l y s t r u c t u r e l e s s l i m e s t o n e . Veins and s h e e t s o f c r y s t a l l i n e c a l c i t e occupying j o i n t s and bedding p l a n e s a r e common, a s a r e i r r e g u l a r p a t c h e s o f t i g h t l y l i t h i f i e d and

o c c a s i o n a l l y b r e c c i a t e d yellow and brown p i p e - f i l l d e p o s i t s .

"Caymanite", f i n e l y bedded impure d o l o m i t i c l i m e s t o n e r a n g i n g i n c o l o u r from w h i t e t h r o u g h r e d and brown t o b l a c k , was n e v e r found on L i t t l e Cayman, though c h a r a c t e r i s t i c o f B l u f f Limestone, a p p a r e n t l y a s a f i s s u r e - f i l l , on b o t h Grand Cayman and Cayman B r a c . Otherwise t h e B l u f f Limestone c l o s e l y r e s e m b l e s t h a t on t h e two l a r g e r i s l a n d s , a t

l e a s t i n hand specimen and t o p o g r a p h i c e x p r e s s i o n . On L i t t l e Cayman, B l u f f Limestone o u t c r o p s on t h e c o a s t o n l y a t t h e e a s t end, where i t forms ramp-like c l i f f s ( P l a t e 9 ) .

The second e x t e n s i v e u n i t on L i t t l e Cayman i s i n t e r p r e t e d a s a Marl o r Sand Ridge F a c i e s of t h e I r o n s h o r e Formation. I n hand specimen i t i s a f i n e - t e x t u r e d cream t o b u f f l i m e s t o n e , m a s s i v e , s t r u c t u r e l e s s , and u s u a l l y l a c k i n g f o s s i l s . f t forms a s o l i d s u r f a c e and i n c o n t r a s t t o t h e B l u f f Limestone o f t e n c a r r i e s a s o i l and l i t t e r c o v e r . I n t h e w e s t e r n lowlands t h e s u r f a c e i s u n d u l a t i n g , w i t h a r e l i e f of 0 . 5 - 1 m , w i t h r e d o r yellow s o i l s , o f t e n p h o s p h a t i c , i n t h e s w a l e s , I n t h e c e n t r a l p a r t o f t h e i s l a n d , s o u t h o f Sparrowhawk H i l l , t h e s u r f a c e i s more uniform and t h e s o i l s d a r k e r , d e e p e r and more c o n t i n u o u s . T h i s u n i t a l s o forms t h e h i g h p e r i p h e r a l r i d g e s , r e a c h i n g a h e i g h t o f 1 3 m above s e a l e v e l , though some r i d g e s , e s p e c i a l l y t h o s e i n t h e n o r t h e a s t , a r e formed o f B l u f f Limestone. Ridges formed o f Sand Ridge f a c i e s have u n d i s s e c t e d s u r f a c e s , and s o i l i s p r e s e n t though t h i n n e r t h a n i n t h e lowlands. I n hand specimen l i t h o l o g y a p p e a r s s i m i l a r i r r e s p e c t i v e o f a 1 ti tu d e

.

The f i e l d r e l a t i o n s o f t h e two u n i t s a r e n o t e a s y t o i n t e r p r e t . L i t t l e Cayman d i f f e r s from Grand Cayman and Cayman B r a c , where t h e r e i s a h i g h c o r e o f B l u f f Limestone s u r r o u n d e d by an apron o f I r o n s h o r e Formation. On L i t t l e Cayman t h e Sand Ridge f a c i e s o f t h e I r o n s h o r e a p p e a r s t o p e n e t r a t e i n t o t h e c e n t r e o f t h e i s l a n d between r i d g e s o f d i s s e c t e d B l u f f Limestone. The h i g h e s t a r e a s s u r v e y e d c o n s i s t o f Sand Ridge f a c i e s , b u t c o n v e r s e l y t h e r e a r e l a r g e a r e a s o f d i s s e c t e d

Bluff Limestone which a r e n o t covered by t h e Sand Ridge o r Marl Facies.

The t r a n s i t i o n between t h e two u n i t s i s o f t e n very abrupt, e s p e c i a l l y i n i n t e r i o r depressions near p r e s e n t sea l e v e l . On f i e l d r e l a t i o n s alone i t i s o f t e n impossible t o be c e r t a i n whether i n t e r i o r karst-eroded depressions c o n s i s t of Bluff Limestone surrounded by Ironshore o r of d i s s e c t e d Ironshore i t s e l f .

The Reef Facies of the Ironshore Formation outcrops t o form c o a s t a l platforms a t S a l t Rocks and immediately south of t h e a i r s t r i p a t t h e west end of the i s l a n d . I t i s a l s o found on t h e seaward s i d e of Owen

I s l a n d i n South Hole Sound, b u t i s absent from the r e s t of the south c o a s t . There a r e low discontinuous exposures on t h e north c o a s t a t Bloody Bay, and a t the e a s t end a t Calabash Spot (Figure 5; P l a t e s 10-12). I n a d d i t i o n t o these c o a s t a l platforms, c o r a l s (mainly M o n t a s t r e a s p e c i e s ) a r e a l s o almost always found i n limestone below

about 1.5 m above sea-level on t h e landward margins of s a l t ponds and s a l t f l a t s ( P l a t e 131, and t h i s may r e p r e s e n t the inner edge of t h e Reef Facies where i t e i t h e r abuts a g a i n s t Bluff Limestone o r passes i n t o back- r e e f f a c i e s . The upper s u r f a c e of the Reef Facies proper stands a t l e s s than 2 m above sea l e v e l a t a l l l o c a t i o n s . I t i s h i g h e s t a t S a l t Rocks, where i t reaches 1.9 m; elsewhere it stands a t l e s s than 1 . 5 m and o f t e n l e s s than 1 m above sea l e v e l , Where higher e l e v a t i o n s a r e found t h e s e a r e on Sand Ridge Facies r a t h e r than Reef Facies.

The c o r a l fauna i s modern, and t h e same a s t h a t of Grand Cayman.

Common components a t S a l t Rocks a r e :

A c r o p o r a p a l m a t a M o n t a s t r e a a n n u l a r i s D i p l o r i a l a b y r i n t h i f o r m i s M o n t a s t r e a c a v e r n o s a D i p l o r i a s t r i g o s a P o r i t e s p o r i t e s M e a n d r i n a s p

.

In the south, the dominant c o r a l i s M o n t a s t r e a a n n u l a r i s , though M . c a v e r n o s a i s a l s o p r e s e n t . S t r o m b u s g i g a s i s conspicuous and l o c a l l y common,

The upper s u r f a c e of the Reef Facies i s h o r i z o n t a l , though deeply d i s s e c t e d i n places by potholes ( P l a t e 1 4 ) ; i t s inner p a r t may be e x f o l i a t i n g and smooth. I t i s probably a d e p o s i t i o n a l r a t h e r than e r o s i o n a l s u r f a c e ,

The c o n t a c t between t h e Reef Facies and the Sand Ridge Facies i s b e s t seen a t S a l t Rocks (935745: Figure 6 ; P l a t e s 15-16). Here t h e h o r i z o n t a l Reef Facies s u r f a c e i s o v e r l a i n by bedded c a l c a r e n i t e s 2 m thick a t t h e i r o u t e r edge. The upper s u r f a c e of the c a l c a r e n i t e r i s e s from 4 t o 5 m above s e a l e v e l i n a d i s t a n c e of 25-35 m before passing beneath a Recent boulder beach; i n l a n d o f the boulder beach t h e s u r f a c e

continues t o r i s e and reaches a h e i g h t of 13 m a t 300 m from t h e sea (Figure 4 A ) . The u n i t has t h r e e components: a b a s a l coarse g r i t w i t h rounded blocks of o o l i t e and S t r o m b u s s h e l l s ; abedded c a l c a r e n i t e showing strong seaward d i p ; and an upper g e n t l y dipping c a l c a r e n i t e forming t h e ground s u r f a c e . Similar b e d d e d o o l i t i c . c a l c a r e n i t e s o v e r l i e Reef Facies i n a comparable l o c a t i o n on Grand Cayman ( a t 589325).

B y comparison w i t h s i m i l a r r e e f s on o t h e r Caribbean i s l a n d s , t h e Reef F a c i e s of t h e I r o n s h o r e Formation i s probably of l a s t i n t e r g l a c i a l age ( c a 125,000 y r )

.

The a s s o c i a t e d f a c i e s a r e probably of broadly comparable l a s t i n t e r g l a c i a l age, though on b o t h Grand Cayman and L i t t l e Cayman t h e Sand Ridge F a c i e s p r e s e n t s problems of i n t e r p r e t a t i o n and chronology.

The p e r i p h e r a l Recent beach r i d g e s ( F i g u r e 7; P l a t e s 17-19) a r e v a r i a b l e i n h e i g h t , width and composition on L i t t l e Cayman. The cobble and r u b b l e r i d g e a t P i r a t e ' s P o i n t (943738) i s 100 m wide and reaches 4 m above sea l e v e l ; i t i s one of t h e l a r g e s t on t h e i s l a n d . Sand r i d g e s and mixed sand and cobble r i d g e s a r e u s u a l l y s m a l l e r . A t t h e West P o i n t l i g h t (933743) t h e r i d g e i s 55 m wide and 3.7 m high; a t Blossom V i l l a g e (960738) t h e dimensions a r e 50 m and 2 m; a t P a r a d i s e End

(046777) 120 m and 2.9 m; and a t Sparrowhawk H i l l (004785) 50 m and 1 . 7 m. A l l t h e s e a r e asymmetric r i d g e s , h i g h e s t near t h e s e a and d e c l i n i n g t o a s a l t pond o r s a l t f l a t on t h e landward s i d e . I n some p r o t e c t e d s i t u a t i o n s , a s a t Bloody Bay (973768), however, t h e r i d g e i s low and f e a t u r e l e s s , forming a h o r i z o n t a l s u r f a c e 150 m wide and 1 . 5 m high. A l l t h e s e r i d g e s a r e probably b u i l t on a p l a t f o r m of I r o n s h o r e Formation a t o r s l i g h t l y below s e a - l e v e l , and i n most c a s e s t h i s p l a t f o r m o u t c r o p s on t h e landward s i d e a s t h e rock f l o o r of s a l t ponds and s a l t f l a t s . The sand and cobble r i d g e a t S a l t Rocks i s unusual i n t h a t it i s perched on high-standing Ironshore about 80 m from t h e s e a ; i t i s about 35 m wide and 2.7 m t h i c k . From Mary's Bay t o Calabash Spot on t h e n o r t h e a s t c o a s t , t h e modern beach r i d g e d i r e c t l y a b u t s t h e Bluff Limestone C l i f f ; t h e r e a r e no s a l t ponds o r f l a t s , and t h e h e i g h t of t h e sand r i d g e i s i n c r e a s e d by dune d e p o s i t s . The r i d g e s a r e wholly formed of r e e f - d e r i v e d c a r b o n a t e s , with t h e exception of l o c a l l y abundant p a t c h e s of d r i f t pumice.

The cobble and rubble r i d g e s a r e c l e a r l y l o c a l i s e d formations

a t t r i b u t a b l e t o major storms; i t i s noteworthy t h a t they a r e a l l s i n g l e f e a t u r e s r a t h e r than sequences of r i d g e s . There a r e a l s o some l a r g e storm b l o c k s , e s p e c i a l l y on t h e southern Ironshore p l a t f o r m hear t h e a i r s t r i p ( P l a t e 2 1 ) . Two l a r g e blocks here measured 1 . 2 x 1 . 5 x 1 . 5 rn and 1 . 8 x 1.5 x 1 . 5 m ,

The sand r i d g e s c o n s i s t of w e l l - s o r t e d carbonate sands i n t h e c o a r s e t o medium sand c a t e g o r i e s ( F i g u r e 8 ) . Beachrock i s n o t common on t h e p r e s e n t beaches, b u t r e l i c t beachrock i s q u i t e e x t e n s i v e l y exposed a few metres from t h e beach f o o t along the south c o a s t .

References

B r u n t , M.A., G i g l i o l i , M.E.C., Mather, J . D . , P i p e r , D.J.W., and

Richards, H . G . 1973. The P l e i s t o c e n e rocks of t h e Cayman I s l a n d s . G e o l . May. 110, 209-221.

Macdonald, K . C . and Holcombe, T . L . 1978. I n v e r s i o n of magnetic anomalies and s e a - f l o o r spreading i n t h e Cayman Trough. E a r t h p l a n e t . S c i . L e t t . 4 0 , 407-414.

Mather, J . D . 1971. A preliminary survey o f t h e groundwater resources o f t h e Cayman Islands with recornendations for t h e i r development.

London: I n s t i t u t e o f G e o l o g i c a l S c i e n c e s , H y d r o g e o l o g i c a l Department

.

M a t l e y , C.A. 1926. The geology o f t h e Cayman I s l a n d s ( B r i t i s h West I n d i e s ) and t h e i r r e l a t i o n t o t h e B a r t l e t t Trough. Quart. J . Geol. Soc. Lond. 8 2 , 352-386.

P e r f i t , M.R. and Heezen, B . C . 1978. The g e o l o g y and e v o l u t i o n o f t h e Cayman Trench. Geol. Soc. Amer. B u l l . 8 9 , 1155-1174.

T a b e r , S . 1922. The g r e a t f a u l t t r o u g h s o f t h e A n t i l l e s . J. Geol.

30, 89-114.

Uchupi, E . 1975. P h y s i o g r a p h y of t h e Gulf o f Mexico and C a r i b b e a n S e a . I n A.E.M. Nairn and F.G. S t e h l i , e d s . : The Ocean Basins and

Margins, 3. The G u l f o f Mexico and the Caribbean (New York:

Plenum)

,

1-64.

Woodroffe, C. and S t o d d a r t , D.R. i n l i t t . Pleistocene h i s t o r y and r e e f and shore morphology i n the Cayman Islands. P a p e r d e l i v e r e d a t t h e T h i r d I n t e r n a t i o n a l Symposium on C o r a l R e e f s , Miami, 1977.

F i g u r e 3, Topography o f L i t t l e Cayman, b a s e d on t h e D i r e c t o r a t e o f O v e r s e a s S u r v e y s 1 : 2 5 , 0 0 0 map (1965)

F _.J

-

^{' ,;2'--./- '':-TI*-.} F-.-.-C---rr--

-y-

*___---T--*-7

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,w 2- * .a I P

r .

- ..

F i g u r e 4 . Topographic t r a v e r s e s A-F: f o r l o c a t i o n s s e e F i g u r e 3

F i g u r e 5 . Geology

beach

F i g u r e 6 . Topographic p r o f i l e s a t S a l t Rocks

metres

1 5 1

metres

Figure 7. Beach r i d g e and c l i f f e d c o a s t p r o f i l e s : f o r l o c a t i o n s s e e Figure 3

Figure 8. S i z e composition of beach sediments

P l a t e 2 . Sparrowhawk H i l l from t h e n o r t h c o a s t beach r i d g e

P l a t e 3 . Limestone r i d g e i n l a n d of t h e c o a s t a l s a l t pond a t C h a r l e s Bight

P l a t e 4 . Limestone r i d g e and c o a s t a l sand f l a t and s a l t pond a t Mary's Bay

P l a t e 5. Dissected s u r f a c e on t h e Bluff Limestone (6032 1783);

t h e s i d e s of t h e frame a r e 50 cm long

P l a t e 7. Large d o l i n e i n Bluff Limestone (6028 1778)

P l a t e 8. Cave speleothems r e v e a l e d by roof c o l l a p s e (6003 1781)

P l a t e 9. Bluff c o a s t a t East P o i n t

P l a t e 10. Ironshore p l a t f o r m west of Calabash Spot

P l a t e 11. D i p l o r i a c o l o n i e s i n c o a s t a l I r o n s h i r e a t S a l t Rocks

P l a t e 12. Strombus s h e l l s i n c o a s t a l I r o n s h o r e a t S a l t Rocks

P l a t e 13. I r o n s h o r e d e p o s i t s on t h e landward margins o f t h e Blossom V i l l a g e lagoon

P l a t e 1 4 . Potholes i n t h e Ironshore surface a t S a l t Rocks

P l a t e 15. Bedded c a l c a r e n i t e s overlying reef f a c i e s i n the Ironshore a t S a l t Rocks

P l a t e 16. D e t a i l of t h e bedded c a l c a r e n i t e s a t S a l t Rocks

P l a t e 1 7 . Beach ridge e a s t of P i r a t e ' s Point

P l a t e 18. Beach r i d g e a t Calabash P o i n t

P l a t e 19. Sand beach r i d g e w i t h j u v e n i l e Casuarina i n Wearis Bay

Blossom Bay

P l a t e 21. Hurricane-deposited storm b l o c k s on t h e I r o n s h o r e p l a t f o r m s o u t h of t h e a i r s t r i p (5957 1737)