﻿1861.] 



KIRKBY PERMIAN, SOUTH YORKSHIRE. 



321 



between the latter and the Durham fauna during the Compact Lime- 

 stone era. It is certainly difficult to attempt comparisons with so 

 small a group of species, which may or may not give a fair idea of 

 the original distribution of life in that area, though I incline to the 

 former opinion. We see, however, the same ascendency of Gastero- 

 pods and Conchifers, and the same rarity of Brachiopods that obtain in 

 the fauna of the Lower Limestone of Yorkshire. And in these respects 

 we might almost argue a similarity of physical conditions prevailing 

 in the two areas. But the absence of Polyzoa and the great redac- 

 tion in the number of species point to a difference as great perhaps 

 as that which existed between the conditions of the Yorkshire and 

 Durham areas. Between the Lancashire and the Durham faunae, that 

 of Yorkshire holds an intermediate place. Its zone of depth, as 

 already remarked, was apparently not so great as that of the Compact 

 Limestone, though decidedly greater than that of the sea of the Lan- 

 cashire area. The fauna of the latter appears to have existed on the 

 argillaceous and semicalcareous submarine mud-flats that lay off the 

 coast of a Permian land-area ; the Yorkshire fauna certainly existed 

 further away in deeper water and within the limits of regular depo- 

 sition of calcareous sediment, though still towards the shallower 

 zones of that region ; the fauna of the Compact Limestone of Dur- 

 ham seems to have dwelt still further seaward, where the depth was 

 greatest. These conclusions are in perfect harmony with the teach- 

 ings of a more comprehensive view of the Permian deposits of Bri- 

 tain ; for an examination of them leads to the opinion that the sea 

 which covered so much of the British area in Permian times, deepened 

 to the north and east and shallowed to the south and west. This we 

 may easily prove by tracing the Permian strata from the north-east 

 corner of Durham south and westward, noting the gradual change 

 from magnesian-calcareous deposits to others which are argillaceous, 

 arenaceous, and conglomeratic, — these lithological changes being 

 likewise accompanied by analogous changes in the distribution of 

 the remains of organic life, there being at the one extreme (Durham) 

 a deep-sea fauna in calcareous strata, and at the other (Bristol) a 

 conglomerate charged with the remains of Beptiles. 



As before stated, the exact horizon of the fossiliferous beds of the 

 Lancashire series has not been determined ; nor is it easy to do so. 

 But it may be suggested that, as the beds in question (which are thin 

 limestones and marls) most probably represent the period of greatest 

 depth of sea attained in the Lancashire area in Permian time, being 

 the only calcareous beds of the series, they may easily be of synchro- 

 nous deposition with the Lower and Compact Limestones, which are 

 considered to be representatives of the same period in their respective 

 areas. This would certainly be the case if the depression of sea-bot- 

 tom, which originated the increased depth of sea, arrived at its maxi- 

 mum in all parts of the British area at the same time : and, so far 

 as we know, there is nothing that seems to disprove that it did ; at 

 least it is much more likely, when we consider the nearness of the 

 Lancashire and Yorkshire areas, that they were affected alike and 

 attained their maximum depth of sea about the same time, than that 



z 2 



