﻿1861.] 



K IKK BY PERMIAN, SOUTH YORKSHIRE. 



315 



individuals. The associated specimens of Bissoa Leighi, Natica 

 minima, and Straparollus Permianus are mature individuals, so far 

 as the development of these species is known to us from their occur- 

 rence in the Permian strata of other districts. The latter, however, 

 are smaller species than the former, and their individuals are of 

 about similar gravities as the immature examples of the first-named 

 species. Hence when we consider their great numbers, smallness, and 

 general uniformity of size, and the comminuted state of the Polyzoa 

 that occur along with them, it seems likely that we have here an 

 instance of the accumulating action of currents. It is easy to 

 understand how a submarine current of a certain power, passing over 

 a sea-bottom strewed with various forms of marine life, could sweep 

 away those organisms whose specific gravities it could overcome to 

 some region more or less distant, where its force became spent or 

 lessened, and there deposit them in quantities as countless as those of 

 Hampole. If its power never exceeded a certain limit, the larger and 

 more weighty organisms would not be removed, while the smaller, if 

 unattached and not otherwise held down, would be carried off ; and 

 supposing the currents were periodical and occurring only at stated 

 seasons, hosts of young shells at a particular stage of development 

 might be swept away at intervals. It must certainly be allowed 

 that the fossils individually show no perceptible traces of such a 

 removal, though to what extent traces of this kind in the shape of 

 abrasion, etc., would be perceptible in the case of transportation over 

 a soft sea-bottom, such as the Lower Limestone in the course of 

 deposition would surely form, does not appear, though we can readily 

 conceive that they would possibly not be very evident. There may 

 be other ways of accounting for the aggregation of so many minute 

 Univalves in one locality ; but I certainly know of none that so well 

 explains the facts of the case as the one suggested. JSbr do I know 

 of any other instance in the Permian deposits of Yorkshire and 

 Durham, where we seem to have such indications of the influence of 

 ancient submarine currents in the distribution or rather accumulation 

 of their organic remains. 



The polyzoan beds also seem to be at first sight an accumulation of 

 drifted materials. This is only a natural surmise on finding so 

 fragmentary an assemblage of remains as those which enter so largely 

 into the composition of these strata. Nevertheless I am disposed to 

 consider them the remains of Polyzoa that lived where we find them, 

 and that the range of the beds marks the site of an ancient ground 

 or zone altogether (or nearly so) peopled by Polyzoa, — where they 

 lived and died generation after generation for a long period, the latter 

 generations growing on a sea-bottom composed of fragments of the 

 polypidomsthatpreceded them.until at last, owing to reasons unknown, 

 their growth ceased after the accumulation of several thick beds of 

 their remains. This I think is proved by the fossils belonging nearly 

 altogether to Polyzoa. Had they been accumulated by the action of 

 a current sweeping over the bottom of the sea, there would surely 

 be observed amongst them a greater mixture of other species, more 

 especially as we know that there were several others which helped 



