Australian Archaeology - CORE

Australian Archaeology

Archived at Flinders University: dspace.flinders.edu.au

Full Citation Details:

Bindon, P. Dortch, C. & Kendrick, G. 1978. A 2500 year old

pseudo shell midden on Longreach Bay, Rottnest Island, Western

Australia. 'Australian Archaeology', no.8, 162-171.

A 2 5 0 0 Y E A R O L D P S E U D O S H E L L M I D D E N ON L O N G R E A C H B A Y , R O T T N E S T I S L A N D , W E S T E R N A U S T R A L I A

P e t e r Bindon C h a r l e s D o r t c h George K e n d r i c k

Introduction

On s e v e r a l o c c a s i o n s d u r i n g t h e p a s t d e c a d e , P e r t h - b a s e d a n d o c c a s i o n a l v i s i t i n g Q u a t e r n a r y r e s e a r c h e r s h a v e examined p o s s i b l e p r e h i s t o r i c human o c c u p a t i o n s i t e s on R o t t n e s t I s l a n d , 2 0 km w e s t of F r e m a n t l e , WA ( F i g . l ) . The f o l l o w i n g d e s c r i b e s f i n d i n g s from r e c e n t i n v e s t i g a t i o n s of p o s s i b l e p r e h i s t o r i c midden m a t e r i a l from a s i t e on Longreach Bay, R o t t n e s t I s l a n d .

The

i s l a n d

R o t t n e s t I s l a n d is t h e l a r g e s t and most n o r t h e r l y o f s e v e r a l i s l a n d s on t h e c o n t i n e n t a l s h e l f n e a r P e r t h . D r P.E. P l a y f o r d h a s r e c e n t l y p u b l i s h e d a summary of t h e i s l a n d ' s g e o l o g y a n d p h y s i o - graphy i n which he d e s c r i b e s t h e 1900 ha i s l a n d a s b e i n g 'composed wholly of Q u a t e r n a r y d e p o s i t s , mainly P l e i s t o c e n e l i m e s t o n e a n d Holocene dune s a n d ' , w i t h a c o a s t l i n e ' c h a r a c t e r i s e d by a l t e r n a t i n g bays and l i m e s t o n e h e a d l a n d s ' ( P l a y f o r d 1977:lO). T o p o g r a p h i c a l l y t h e i s l a n d i s dominated by l i m e s t o n e h i l l s and s a n d d u n e s . T h e r e i s a s e r i e s o f s a l t l a k e s i n t h e n o r t h e a s t e r n p a r t o f t h e i s l a n d and b e f o r e e x t e n s i v e modern development t h e i s l a n d c o n t a i n e d a number of s m a l l f r e s h w a t e r swamps. The c a l c a r e o u s s o i l s of t h e i s l a n d a r e v e r y w e l l d r a i n e d . S u r f a c e f r e s h w a t e r i s now v i r t u a l l y a b s e n t , e x c e p t a r o u n d t h e m a r g i n s o f t h e s a l t l a k e s where P l a y f o r d n o t e s ' ~ u r n e r o u s s m a l l f r e s h - t o - b r a c k i s h - w a t e r s e e p a g e s ' (1977:lO).

The o r i g i n a l v e g e t a t i o n , now v e r y l a r g e l y d e s t r o y e d , c o n s i s t e d o f f o r e s t s of t i - t r e e s , w a t t l e s and R o t t n e s t I s l a n d P i n e (CaZZitris p r e i s i i ) , and a r e a s of open h e a t h ( S t o r r e t aZ. 1 9 5 9 ) . I t h a s been e s t i m a t e d t h a t n a t i v e f o r e s t , which now c o v e r s o n l y 5% o f t h e i s l a n d , once o c c u p i e d 65% ( P l a y f o r d 1977: 1 0 ) .

S h o r e l i n e f e a t u r e s on t h e i s l a n d h a v e o f t e n b e e n c i t e d i n s t u d i e s of Q u a t e r n a r y e u s t a t i c s e a l e v e l c h a n g e s ( e

.

g. F a i r b r i d g e 1961). Evidence now s u g g e s t s t h a t l i m e s t o n e r e e f p l a t f o r m s and wave-cut n o t c h e s , a s much a s 3 m above p r e s e n t s e a l e v e l , e a r l i e r

t h o u g h t t o b e formed s o l e l y by e u s t a t i c h i g h s e a l e v e l s ( F a i r b r i d g e 1961; T e i c h e r t 1 9 5 0 ) , may i n s t e a d be p a r t l y t h e r e s u l t o f l o c a l t e c t o n i c u p l i f t ( P l a y f o r d 1977:32, 34, 3 7 ) .

Marine s h e l l b e d s exposed on o l d s h o r e l i n e s a r o u n d t h e s a l t l a k e s a r e t h o u g h t t o have been d e p o s i t e d d u r i n g mid-Holocene h i g h s c n l e v e l s . ( F o r d i s c u s s i o n of p o s s i b l e mid-Holocene t e c t o n i s m and e u s t a t i c s e a l e v e l changes s e e P l a y f o r d 1977 a n d P l a y f o r d e t al.

i n p r e s s . ) These s h e l l b e d s have more t h a n o n c e b e e n m i s t a k e n f o r middens, a s have a c c u m u l a t i o n s of s h e l l s removed from t h e b e d s a n d used f o r r o a d - b u i l d i n g i n o t h e r p a r t s of t h e i s l a n d .

S W A N

T h e r e a r e o t h e r , sometimes m o n o s p e c i f i c s h e l l h e a p s on v a r i o u s l i m e s t o n e h e a d l a n d s around t h e i s l a n d . T h e s e t a o h a v e been

i n t e r p r e t e d a s p o s s i b l e middens, though a t p r e s e n t no a r c h a e o l o g i c a l m a t e r i a l i s known from any o f t h e s e t o s u p p o r t s u c h a n i n t e r p r e t a t i o n .

Aboriginal occupation

T h e r e i s no e v i d e n c e f o r p r e h i s t o r i c A b o r i g i n a l o c c u p a t i o n o f R o t t n e s t I s l a n d ; and i t i s g e n e r a l l y f e l t t h a t t h e i s l a n d was n o t o c c u p i e d by A b o r i g i n e s a f t e r h a v i n g been c u t o f f by r i s i n g s e a s a b o u t 6500 y e a r s ago ( C h u r c h i l l 1959:Fig. 2; T e i c h e r t 1 9 5 9 ) . The p r e s e n t l a c k of any a r c h a e o l o g i c a l m a t e r i a l of e a r l y Holocene o r l a t e P l e i s r o c e n e a g e seems s u r p r i s i n g b e c a u s e i n some ways t h e i s l a n d p r o b a b l y was always e x p l o i t a b l e by h u n t e r - g a t h e r e r s . A t t i m e s o f low s e a l e v e l t h e i s l a n d would h a v e b e e n a s e r i e s o f d e n s e l y v e g e t a t e d , e l e v a t e d d u n e s and r i d g e s p r o b a b l y h a r b o u r i n g a v a r i e t y of game. The p r e s e n t s a l t l a k e s would h a v e b e e n d e e p l y e x c a v a t e d k a r s t f e a t u r e s ( P l a y f o r d 1977 : 3 7 ) . P l a u s i b l e s i t u a t i o n s f o r l a t e g l a c i a l and e a r l y Holocene o c c u p a t i o n s i t e s e x i s t i n t h e m a r i n e , l a c u s t r i n e and a e o l i a n d e p o s i t s now found i n t h e v i c i n i t y . of t h e s a l t l a k e s and swamps. Another a r e a l i k e l y t o h a v e b e e n occupied a t t h i s time i s now o f f - s h o r e between t h e i s l a n d a n d t h e l a t e g l a c i a l t o e a r l y Holocene c h a n n e l o f t h e Swan E s t u a r y , 8-10 km t o t h e n o r t h ( F i g . l , i n s e t ) .

The o n l y known A b o r i g i n a l o c c u p a t i o n o f t h e i s l a n d t o o k p l a c e between 1838 and 1931 when t h e c o l o n y , a n d l a t e r , t h e s t a t e o f Western A u s t r a l i a m a i n t a i n e d a p r i s o n s p e c i f i c a l l y f o r A b o r i g i n e s

( S o m e r v i l l e 1 9 4 9 ) . During t h e l a t t e r h a l f o f i t s t r a g i c e x i s t e n c e t h i s p r i s o n h e l d numerous A b o r i g i n a l men, i n c l u d i n g some f r o m t h e Kimberley d i s t r i c t who had been t r a n s p o r t e d 2000 km s o u t h w a r d from Broome t o s e r v e t h e i r s e n t e n c e s . The A b o r i g i n e s w e r e a l l o w e d

l i m i t e d f o r a g i n g r i g h t s on t h e i s l a n d by t h e more l e n i e n t g o v e r n o r s . The p r i n c i p a l game was p r o b a b l y quokkas ( a s p e c i e s of r a t - k a n g a r o o

from which t h e i s l a n d r e c e i v e s i t s name) a n d w a t e r f o w l ; a n d t h e weapons used were s p e a r and boomerang ( S o m e r v i l l e 1 9 4 9 ) . S o m e r v i l l e a l s o r e c o r d s t h a t f i s h were t a k e n w i t h hook and l i n e ; h e d o e s n o t r e c o r d s h e l l f i s h g a t h e r i n g , though many o f ' t h e p r i s o n e r s from c o a s t a l a r e a s i n t h e n o r t h c ~ e s t must have b e e n aware of t h i s s o u r c e of food.

The Kimberley i n m a t e s a t l e a s t , u s e d s p e a r s armed w i t h b i - f a c i a l l y f l a k e d g l a s s p o i n t s . Numbers of g l a s s b i f a c i a l p o i n t s , i n v a s i v e l y f l a k e d and t y p i c a l o f t h e

'

~ i m b e r l e y

'

form (McCarthy 1967:Fig.22), have been found on t h e e a s t e r n e n d of t h e i s l a n d

( S e r v e n t y 1 9 6 7 ) . One of t h e s e , c o l l e c t e d some 300 m s o u t h o f t h e Longreach Bay S i t e ( F i g . 1 ) by D r R. H o r w i t z , CSIRO, P e r t h , i s i l l u s t r a t e d i n F i g u r e 2.2.

The Longreach Bay

s i t e ( N a t i o n a l g r i d r e f e r e n c e : S1 50-2 35130436) The s i t e i s l o c a t e d on a wave-cut b e n c h i n a s m a l l h e a d l a n d of Tamala Limes tone ( P l a y f o r d 1977: 1 3 ) which f o r m s t h e e a s t e r n e n d of Longreach Bay ( F i g s 1, 3 ) . \Je f i r s t i n v e s t i g a t e d t h e s i t e a s a p o s s i b l e s h e l l midden l e f t by f o r a g i n g A b o r i g i n a l p r i s o n e r s . T h i s

Fig. 2 Flaked glass artifacts from Rottnest Island, W.A.

was s u g g e s t e d by a h e a p o f l i m e s t o n e f r a g m e n t s , t u r b a n and o t h e r m a r i n e s h e l l s , c h a r c o a l and a r t e f a c t s l y i n g i n a d e p r e s s i o n a t t h e s e a w a r d e n d o f t h e bench. T h i s d e p o s i t , which c o n t a i n e d a few p i e c e s o f f l a k e d g l a s s ( f l a k e s e . g . Fig.2.5), and p a r t s of a u n i f a c e g l a s s p o i n t ( F i g . 2.1)

,

was found t o b e t h o r o u g h l y d i s t u r b e d . Contemporary a r t e f a c t s ( e . g. c i g a r e t t e f i l t e r s ) o c c u r r e d below l a t e 1 9 t h o r e a r l y 2 0 t h c e n t u r y f l a k e d g l a s s . We s u g g e s t t h a t t h e d e p o s i t was n o t a midden ( i . e . an a r c h a e o l o g i c a l d e p o s i t i n p r i m a r y p o s i t i o n ) , b u t i n s t e a d a l a r g e l y n a t u r a l l y a c c u m u l a t e d h e a p of d e b r i s t r a n s p o r t e d by g r a v i t y and w a t e r a c t i o n . Water a c t i o n h e r e r e f e r s o n l y t o run-off from r a i n o r o c c a s i o n a l heavy s p r a y from l a r g e waves, b e c a u s e a t p r e s e n t t h e s u r f a c e o f

t h e bench seems w e l l above t h e s p l a s h zone.

F u r t h e r e x a m i n a t i o n of t h e s i t e showed a d e p o s i t l y i n g w i t h i n a p r o m i n e n t n o t c h a n d o v e r h a n g i n g v i s o r a t t h e landward end o f t h e

bench. A

f o l l o w i n g

t e s t p i t dug i n t o t h i s d e p o s i t i n J u n e 1977 r e v e a l e d t h e s e q u e n c e .

D i r t y g r e y s a n d w i t h t u r b a n and o t h e r marine s h e l l s , c h a r c o a l , and a r t e f a c t s i n c l u d i n g b o t h f l a k e d g l a s s d a t i n g t o t h e p r i s o n p e r i o d , and contemporary a r t e f a c t s s u c h a s aluminium r i n g p u l l s from d r i n k c a n s . The s h e l l s a r e i d e n t i f i e d a s f o l l o w s :

Turbo (Mamarostoma) puZcher

Reeve

Hipponix (Sabia) conicus

(Schumacher) g a s t r o p o d f r a g m e n t s , i n d e t e r m i n a b l e

C l e a n c a l c a r e o u s sand and s h e l l g r i t c o n t a i n i n g t u r b a n and o t h e r s h e l l s , and a n g u l a r r o o f f a l l fragments b u t n o c h a r c o a l o r a r t e f a c t s of any k i n d . S h e l l s i d e n t i f i e d a r e a s f o l l o w s :

Turbo (Mamrostoma) pu Zcher

Reeve

Hipponix (Sabia) conicus

(Schumacher)

Turbo (NineZZal w h i t l e y i

( I r e d a l e )

A zone o f l i m e s t o n e s l a b s w e i g h i n g up t o s e v e r a l k g i n a m a t r i x o f c l e a n s a n d and g r i t . No s h e l l s were c o l l e c t e d i n t h i s zone.

Turban and a few o t h e r s h e l l s i n c l e a n s a n d and s h e l l g r i t , r e s t i n g on smooth l i m e s t o n e bedrock. S h e l l s a r e i d e n t i f i e d a s f o l l o w s :

B i v a l v e

Brachidontes u s t u l a t u s

(Lamarck) G a s t r o p o d s

Acmaea (Notoacmea) o n y c h i t i s

(Merke)

*Turbo (Marmaros toma) puZcher

Reeve

Campani l e symboZicwn

I r e d a l e

Hipponix (Sabia) conicus

(Schumacher)

Nuce ZZa (Dicatha.is) o r b i t a

(Gmelin)

A most common s p e c i e s

A 250 gm sample o f t u r b a n (T. puleher) s h e l l s from t h e 35-50 cm zone o f t h e d e p o s i t was s u b m i t t e d t o t h e U n i v e r s i t y o f Sydney

Radiocarbon L a b o r a t o r y f o r a s s a y and y i e l d e d a d a t e o f 2560

+

1 0 5 BP (SUA-772). X-ray d i f f r a c t i o n a n a l y s i s showed t h a t t h e s h e l l s u b m i t t e d f o r d a t i n g was composed o f a r a g o n i t e , and t h a t no c a l c i t e was

d e t e c t a b l e . Thus t h e above d a t e i s i n o r d e r , s i n c e t h e r e is no e v i d e n c e f o r r e c r y s t a l l i s a t i o n o f t h e s h e l l c a r b o n a t e (WA Government Chemical L a b o r a t o r y R e p o r t No. 61521-2/77)

.

T h i s d e p o s i t seemed o f p a r t i c u l a r i n t e r e s t f o r t h e f o l l o w i n g r e a s o n s .

1. I t was s h e l t e r e d , s o p r e c l u d i n g t h e p o s s i b i l i t y t h a t t h e s h e l l had accumulated t h r o u g h b e i n g dropped by P a c i f i c G u l l s , as r e c o r d e d a t s e v e r a l R o t t n e s t I s l a n d s h o r e l i n e l o c a l i t i e s by T e i c h e r t and S e r v e n t y (1947)

.

2. The marked predominance o f w e l l p r e s e r v e d t u r b a n s h e l l s seemed t o i n d i c a t e a human o r i g i n b e c a u s e middens a r e o f t e n dominated b y a s i n g l e s p e c i e s . F u r t h e r m o r e most of t h e t u r b a n s h e l l s were b r o k e n , and t h e i r a n g u l a r f r a c t u r e s were n o t i n a c c o r d a n c e w i t h n a t u r a l wear and w e a t h e r i n g .

3. The p r e s e n c e o f f l a k e d b o t t l e g l a s s w i t h i n t h e u p p e r few c e n t i m e t r e s

.

These f a c t s l e d us t o b e l i e v e t h a t t h e s i t e was l i k e l y t o b e a modern midden d a t i n g from t h e p r i s o n e r a . The 2500 BP d a t e was unexpected because t h e r e was no p r e v i o u s e v i d e n c e t o s u g g e s t A b o r i g i n a l o c c u p a t i o n on t h e i s l a n d a t t h a t t i m e . F o r t h i s r e a s o n t h e s i t e was a g a i n examined i n March 1 9 7 8 w i t h t h e p u r p o s e o f d e t e r m i n i n g w h e t h e r i t was i n f a c t a p r e h i s t o r i c a r c h a e o l o g i c a l d e p o s i t .

A s m a l l 50 cm s q u a r e t e s t p i t a d j a c e n t t o t h e 1977 e x c a v a t i o n r e v e a l e d t h e f o l l o w i n g sequence :

0-10 cm D i s t u r b e d d i r t y g r e y s a n d w i t h c h a r c o a l , f l a k e d g l a s s , modern a r t e f a c t s , c h a r c o a l , s h e l l s , and o t h e r m a r i n e remains.

10-30 cm Clean c a l c a r e o u s s a n d and s h e l l g r i t , w h o l e t u r b a n s h e l l s , s h e l l f r a g m e n t s , and a n g u l a r l i m e s t o n e b l o c k s , presumably r o o f f a l l . I n t h e l o w e r 1 5 cm o f t h i s zone t h e l i m e s t o n e f r a g m e n t s were r o u n d e d , a n d h e a v i l y abraded.

30-40 cm Beneath t h e rounded roof f a l l f r a g m e n t s whole t u r b a n s h e l l s were r e l a t i v e l y s c a r c e , and s m a l l s h e l l f r a g m e n t s predominated. The l a s t 3 cm c o n s i s t e d of s h e l l g r i t and v e r y f i n e s a n d r e s t i n g on smooth l i m e s t o n e bedrock.

The 1978 e x c a v a t i o n r e v e a l e d t h r e e a d d i t i o n s t o t h e s h e l l s u i t e i d e n t i f i e d i n t h e 1977 e x c a v a t i o n .

B i v a l v e

KateZysia scalarina

(Lamarck)

p r o b a b l y a mid-Holocene f o s s i l d e r i v e d from t h e l a k e s . G a s t r o p o d s

Acmaea

(Pate Z Zoida) aZticostata

(Angas)

L i t t o r i m (AustroZittorinal unifasciata

ray)

Below 1 0 cm i n t h i s e x c a v a t i o n , a s i n t h e 1977 p i t , t h e r e were no a r t e f a c t s , c h a r c o a l o r o t h e r e v i d e n c e of human o c c u p a t i o n . Discussion

The 1977 i n v e s t i g a t i o n s i n c o n j u n c t i o n w i t h t h e 2500 BP d a t e s u g g e s t e d t h a t t h e Longreach Bay s i t e was p o s s i b l y a p r e h i s t o r i c A b o r i g i n a l midden. T h i s i n t e r p r e t a t i o n o f t h e d e p o s i t was made p a r t l y b e c a u s e i t d i d n o t resemble an a c c u m u l a t i o n o f r o l l e d s h e l l s and p e b b l e s a s a r e commonly found around rocky s h o r e s on R o t t n e s t I s l a n d . The r e s u l t s o f t h e 1978 e x c a v a t i o n have a l t e r e d t h i s i n t e r p r e t a t i o n o f t h e d e p o s i t . The f a c t o r s t h a t h a v e i n f l u e n c e d t h i s r e v i s i o n i n c l u d e t h e a b s e n c e o f c h a r c a o l and c u l t u r a l m a t e r i a l below a d e p t h of 10 cm; t h e l a c k of any e v i d e n c e on t h e s h e l l s f o r t h e i r h a v i n g b e e n b u r n t , which may be s i g n i f i c a n t a s A b o r i g i n e s h a b i t u a l l y cook s h e l l f i s h b e f o r e consumption; and t h e p r e s e n c e of t h e rounded l i m e s t o n e f r a g m e n t s towards t h e b a s e o f t h e d e p o s i t . The s i g n i f i c a n c e o f t h e d i f f e r e n c e i n t h e l i m e s t o n e fragments from t h e t o p t o b o t t o m o f t h e d e p o s i t had n o t been r e a l i s e d i n t h e 1977 e x c a v a t i o n . The rounded r o c k s a r e n o t roof f a l l b u t r e e f c o b b l e s showing m a r i n e worm b o r i n g s . These r e l a t e t o t h e p e r i o d when t h e bench w a s c u t , presumably d u r i n g t h e middle Holocene ( P l a y f o r d 1977:32, 34, 3 7 ) .

T a k i n g i n t o a c c o u n t t h e p o s s i b i l i t y t h a t t h e s h e l l s i n t h e d e p o s i t a r e t h e r e m a i n s o f a re-worked midden (Hughes and S u l l i v a n 1 9 7 4 ) , we c o n s i d e r t h a t i t i s a n a t u r a l a c c u m u l a t i o n o f s h e l l s i n which t h e s m a l l e r , s o f t e r s h e l l component towards t h e b a s e h a s been r e d u c e d t o g r i t by a t t r i t i o n . We b e l i e v e t h a t t h e rounding and s o r t i n g s e e n i n t h e lower p a r t of t h e d e p o s i t p r o b a b l y

r e p r e s e n t s a t i m e o f h i g h e r s e a l e v e l when h i g h e n e r g y wave s u r g e c a u s e d some a b r a s i o n o f t h e l a r g e l i m e s t o n e f r a g m e n t s , t h e

d e s t r u c t i o n o f s m a l l s h e l l s and t h e p a r t i a l f r a c t u r i n g o f t h e more r o b u s t s h e l l s . The s o r t i n g o f t h e s h e l l s , g r i t and s a n d i n t h e d e p o s i t b e t w e e n 25 cm a n d 50 cm i n d i c a t e s t h a t t h e d e p o s i t i o n of t h i s m a t e r i a l p r o b a b l y took p l a c e c o n t i n u a l l y , and i n a l i t t o r a l s i t u a t i o n . I t must b e p o i n t e d o u t , however, t h a t t h e upper p a r t o f t h e s h e l l component i n c l u d e s v e r y s m a l l s h e l l s and a n g u l a r f r a g m e n t s i n c o n s i s t e n t w i t h a n e x t e n d e d p e r i o d of t u m b l i n g i n a wave z o n e and more c h a r a c t e r i s t i c of f r a c t u r e p a t t e r n s s e e n i n

s h e l l s i n s t o r m b e a c h e s o r middens. We s u g g e s t t h a t t h e d e p o s i t a c c u m u l a t e d o v e r a r e l a t i v e l y b r i e f p e r i o d though we a r e u n c e r t a i n o f t h e way i n which t h e l a r g e s h e l l s were b r o k e n . The p o s s i b i l i t y o f t h e d e p o s i t b e i n g a s t o r m beach seems u n l i k e l y , b e c a u s e o f i t s s o r t i n g a n d i t s f e w s h e l l s p e c i e s . The p r e s e n c e of c h a r c o a l i n t h e u p p e r l e v e l s shows t h a t f i r e s have been l i t on t o p o f t h e d e p o s i t , and t h i s may a c c o u n t f o r some o f t h e a n g u l a r f r a c t u r e of

t h e s h e l l s . However t h e h e a t produced b y t h e s e f i r e s would n o t p e n e t r a t e d e e p e r t h a n s e v e r a l c e n t i m e t r e s , a n d c o u l d n o t h a v e caused t h e a n g u l a r f r a c t u r e p a t t e r n s e e n below t h e zone o f r o o f f a l l .

I t a p p e a r s l i k e l y t h a t t h e l i m e s t o n e s l a b s t o w a r d s t h e b a s e had become a t l e a s t p a r t i a l l y rounded by wave a c t i o n p r i o r t o t h e d e p o s i t i o n o f t h e s h e l l m a t e r i a l .

Concl us i ons

I t seems l i k e l y t h a t most o f t h e s h e l l component i n t h e

d e p o s i t was s t r a n d e d d u r i n g a n e v e n t when wave a c t i o n was s u f f i c i e n t t o produce a d e p o s i t w i t h t h e whole s h e l l component o f a s t o r m beach and t h e s o r t i n g c h a r a c t e r i s t i c o f t h e r o l l e d s h e l l and p e b b l e a c c u m u l a t i o n s mentioned p r e v i o u s l y . We c a n n o t p r e c l u d e t h e p o s s i - b i l i t y t h a t t h e s u r f a c e zone o f t h e s h e l t e r e d d e p o s i t r e p r e s e n t s t h e remains of a s h e l l f i s h midden from t h e p r i s o n e r a . What i s c l e a r , however, i s t h a t A b o r i g i n a l p r i s o n e r s m a n u f a c t u r e d g l a s s b i f a c i a l p o i n t s w h i l e s i t t i n g i n t h e s h e l t e r . S m a l l d e l i c a t e f l a k e s a n d b l a d e l e t s w i t h l i n e a r b u t t s , t y p i c a l o f t h o s e p r o d u c e d i n p r e s s u r e f l a k i n g , and a t l e a s t one l a r g e p r e s s u r e f l a k e d g l a s s f r a g m e n t ( F i g s 2 . 3 , 4 , 6 ) p r o v i d e e v i d e n c e f o r t h i s a c t i v i t y .

We t h e r e f o r e c o n c l u d e t h a t t h e d e p o s i t i s a s p e a r h e a d m a n u f a c t u r i n g s i t e o v e r l y i n g a n a t u r a l l y accumulated s h e l l d e p o s i t .

Acknowledgements

We t h a n k MS B. Wilson f o r h e l p w i t h t h e d r a w i n g o f t h e f i g u r e s , and MS E. B l o o r f o r r e a d i n g t h e MS. W e acknowledge w i t h t h a n k s t h e h e l p g i v e n by Mme D. de S o n n e v i l l e - B o r d e s and M r W. F e r g u s o n d u r i n g t h e 1978 e x c a v a t i o n .

References

C h u r c h i l l , D.M. 1959 L a t e Q u a t e r n a r y e u s t a t i c c h a n g e s i n t h e Swan R i v e r d i s t r i c t .

Journal o f the Royal Society o f Western Australia

42 : 53-5

F a i r b r i d g e , R.W. 1 9 6 1 E u s t a t i c changes i n s e a l e v e l . I n

Physics

and

chemistry of the earth.

Pergamon: London. Pp. 99-185 Hughes, P. J. and M.E. S u l l i v a n 1974 The r e - d e p o s i t i o n o f midden

m a t e r i a l by s t o r m waves.

Journal o f the Royal Society o f N e w South Wales

107 :6-10

McCarthy

,

F. D. 1969

Australian Aboriginal stone impZemnts.

The A u s t r a l i a n Museum: Sydney

P l a y f o r d , P.E. 1977 Geology and groundwater p o t e n t i a l . ^' I n P.E. P l a y f o r d a n d R . E . J . Leech,

G ~ o l o g y and hydrology o f

Rottnest

Island.

G e o l o g i c a l s u r v e y o f Western A u s t r a l i a R e p o r t 6

A.E. Cockbain and G.H. Low ( i n p r e s s ) Geology of t h e P e r t h B a s i n , ^Western A u s t r a l i a .

Western Australian GeoZogicaZ Survey B u l l e t i n

124

S e r v e n t y , P.E. 1 9 6 7 A b o r i g i n a l a r t i f a c t s on R o t t n e s t I s l a n d . W.A.

NaturaZist

10:123-4

S o m e r v i l l e , W. 1949

R o t t n e s t Island.

R o t t n e s t I s l a n d Board of C o n t r o l s p e c i a l p u b l i c a t i o n

S t o r r , G.M., J . W . Green and D.M. C h u r c h i l l 1959 The v e g e t a t i o n o f R o t t n e s t I s l a n d .

JournaZ o f t h e Royal Society o f Western AustraZia

42:70

T e i c h e r t , C. 1950 L a t e Q u a t e r n a r y s e a l e v e l changes a t R o t t n e s t I s l a n d , Western A u s t r a l i a .

Proceedings o f t h e Royal S o c i e t y o f Victor&x

59 : 6 3- 79

and D.L. S e r v e n t y 1947 D e p o s i t s o f s h e l l s t r a n s p o r t e d by b i r d s .

American Journal o f Science

245:322-32

Western Australian Musewn

Perth

WA 6000