37S Transaciions. — Geology. 



below the surface. Some of this also was examined by Mr. 

 Maskell, whose decision as to the fossil natm^'e of the species 

 forming this part of the deposit has already been stated. 

 Subsequently samples were forwarded to England, and ex- 

 amined by one of the chief authorities on diatoms, whose 

 decision was in accordance with the conclusion Mr. Maskell 

 had already arrived at. 



Such are the facts of the case, and such the conclusions 

 arrived at by competent authorities. And yet I am not 

 satisfied that the true explanation has been hit upon ; and 

 here I venture a theory of explanation to which objections 

 may possibly be raised as grave as those which he against 

 Mr. Maskell's theory, yet they are in a different cate- 

 gory : and I have written this paper so that the Society 

 ma}' hcive an opportunity of debating the probabilities of 

 each. 



Considering the conditions under which the diatomaceous 

 deposit has aceumulcited, it is reasonable to expect that recent 

 forms of diatoms would be found in the lowest, as well as the 

 highest, beds of the deposit ; and it is certainly surprising 

 that the upper beds, or latest part of the deposit, should be 

 wholly composed of recent species which are absent from the 

 middle and lower parts. It is quite a possibiht}- that the 

 fossil species forming the bulk of the deposit have been derived 

 from an older deposit, either forming the bed of the lake or 

 now buried beneath the scoria hills to the east of Paeroa. 

 But it seems to me that, in order to account for the facts of 

 the case, it must be supposed that at first onl}' fossil species 

 carried along the undergi-ound channel were deposited in the 

 little basin whence the specimens were obtained. And, as 

 the deposit is enthely composed of fossil species to within 1ft. 

 of the present suiface, the introduction or appearance of living 

 forms is of verj" recent date. 



As, however, the whole deposit is manifestly of quite recent 

 date, and as at first the conditions were as fit for the existence 

 of recent forms of diatoms as they now are, it seems extraor- 

 dinary that throughout the deposit there is not a mixture of 

 fossil and living species. 



Taking these facts into account, I would prefer to account 

 for the difference in the species found in the top and bottom 

 beds of the deposit by supposing that the species first living 

 in the pond gave place to other forms, either modified descend- 

 ants of the original species or species introduced from a different 

 stock, and in this way would avoid the necessity of hypothe- 

 cating an older deposit, the existence of which has not been 

 proved, and, at the same time, accounting for the separateness 

 of the living and extinct forms as they are found in the higher 

 and lower parts of the deposit. 



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