32 



E\^DENCES OF THE SHELL DEPOSITS 



SEEN AROUND THIS CITT, NOT BEING PRODUCED BY THE ABORIGINES, AND 

 THE PERIOD OF THEIR ORIGIN BEING POST TERTIARY. 



[Read by H. S. Wintle, 12th April, 1864.] 



A PAPER which I read before this Society, in Xovember last, on what I was then 

 pleased to consider,aud still believe to be, post tertiary marine deposits, having 

 called forth expressions of strong doubt with regard to the position I assigned 

 to them in geological scale, and also to the mode of their origin, I here beg to 

 furnish the data on which I base the conclusions therein set forth, and which I 

 think will show that such conclusions are not so rash or premature as may have 

 been imagined. 



In a vertical section of these shell-beds exposed in the face of a cliff forming 

 part of the river-bank at Sandy Bay, and which was referred to at some length 

 in the paper just mentioned, the folloAving order of strata is met with : — ■ 



First. — A lie 1 of rich vegetable soil, po?sessing an average depth of 18 inches, 

 in whicli no shells are seen, but containing fragments of charcoal, &;c. 



Secondly.— A stratum of comminuted shells, all of recent spacies, imbedded 

 in a coarse black sandy soil. Average depth, 2 feet; and containing small 

 quartz, and greenstone pebbles. No charcoal. 



Thirdly.— A stratum of large rounded pebbles derived from the adjacent 

 felspathic trap, and greenstone, with occasionally pebbles of sandstone — thinly 

 interspersed with very small fragments of the over-lying shells. 



Fourthly. — A stratum of comminuted shells of recent species, same as above. 

 Average depth, 1 foot. 



Fifthly. — A thin stratum of marl reposing upon what I believe to be the 

 equivalent of the English New Red Sandstone. 



Now let us enquire under what circumstances the formation of these several 

 beds took place, and examine one by one in the ascending order, commencing 

 with the marl, which forms the lowest stratum of the series. Whether this 

 marl is of marine, or fresh water orign, there is no direct evidence to show ; 

 but there is sufficient evidence to prove it was formed in still water at some 

 considerable depth. This is not the case with the shell bed reposing on it, for 

 that unmistakeably proves that the shells originally occupied a zone not far 

 from the shore, and where the water was more or less agitated, as seen by the 

 water-worn fragments of contiguous rocks associated with them. Here, then, 

 is a change seen in the relative position of land and sea. That portion of the 

 sea bed— assuming the marl to be of marine origin— is found at a later period 

 to be close to the shore. Or if of fresh water-origin, gives evidence of the land 

 having subsided beneath the sea-level. The bed of pebbles, some of them 

 being actual boulders, argues a stiU more disturbed state of the water. These 

 pebbles may have been deposited either by tidal action, or by an ancient 

 rivulet having gceat force at certain periods. But they speak in favor of the 

 former action as being the most probable cause, owing to the order of their 

 arrangement. Immediately resting on this bed we have the first stratum of 

 shells, showing that if the pebbles were strewn over a beach, of which there is 

 very little doubt, another sinking of the land took place in order that they 

 might be covered by another generation of testacea. Then a final elevation to 

 be covered by eighteen inches of vegetable mould. 



Assuming that the foregoing hypothesis is inadmissable, and that these'shell- 

 beds are the work of the aborigines, let us ask what could have induced them 

 to spread the shells so uniformly over any given area ?— and what possible 

 motive could they have had in collecting such minute specimens as these I lay 

 before you ? The first-formed bed, it will be remembered, rests upon marl. 

 Allowing this to be as hard and dry, as we find it now, at the time when the 

 blacks were supposed to camp there, we have no evidence to show that it was 

 an easy distance from the water. Facts go to prove that, on the contrary, it 

 was under water at the time of the shell deposit. 



My reason for assigning to these deposits a post tertiary origin is, that in no 

 instance have I found the uppermost bed covered by strata of probable tertiary 

 age, and further, that apart from the recent character of the sheUs, their con- 

 dition favors the inference of their being the equivalent of the post tertiary 

 beds of Europe. 



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