276 NATURAL SCIENCE. Oct.. 1895- 



are described as frequent or common associations which can be 

 paralleled to-day from most of the deep-sea soundings, though they 

 are not to be found grouped together at depths beyond 1,000 fathoms. 



At this depth in the North Atlantic the above-named three 

 species occur together, accompanied by all the above-named genera, 

 except Anomalina and Tnincatiilina ; though off the Azores these latter 

 have been obtained at the same depth. Off Pernambuco, at a depth 

 of 675 fathoms, every one of these genera is found grouped, two of 

 the three species being again present. 



The same holds good of the particularly rich ooze off Culebra 

 Island, a centre where the deep-sea and shallow water forms seem to 

 become most intimately intermingled. Below the depth of 1,000 

 fathoms no such associations have been discovered, and, taking into 

 account these facts and the general aspect of the commoner fauna of 

 this chalk, I am led to venture the opinion that it has been laid down 

 at a depth over 400 and under 1,000 fathoms. 



Again, of the rare species which have already been mentioned as 

 very common in the Chalk Marl, a few reappear which are usually 

 absent in the higher zones, viz., Textularia turns, Spiropleda amiectens, 

 and Tritaxia tricavinata; but, in addition, there are a number of others 

 specifically identical with forms now occurring at depths greater than 

 400 fathoms. 



A consideration of these various facts seems to force upon us the 

 conclusion that events had occurred resulting in the reappearance of 

 a shallower fauna, but that Chalk Marl conditions had never been 

 absolutely reestablished. Mr, Chapman is of opinion that the Swans- 

 combe specimens probably came from the Micraster cov-testiidinaniim 

 zone, at whose base is the Chalk Rock. This latter shows in its 

 character such evident traces of change in the direction of elevation 

 that the faunal peculiarities observed may be regarded as additional 

 proof of upward movement at this period. Thus we may conclude 

 that during periods of elevation shallow water faunas extend their 

 range, the extent of such range being the measure of such elevation. 



Hitherto we have been dealing with a fauna which, however 

 interesting in itself, might by many be considered as too minute in 

 character for general study, demanding, as it does, not only pains- 

 taking research, but the direct aid of an expert in specific determina- 

 tion. We will, therefore, next turn to the evidence of a richer and 

 larger fauna as represented in the Mollusca ; and although parallelism 

 by species is out of the question, yet some idea of sequence may be 

 gathered from its study. 



W. F. Hume. 

 {To he continued.) 



