454 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



which are supposed to have been removed are really represented, both 

 around the edge and within the borders of the Coal-basin, though 

 under conditions most remarkable and abnormal when compared with 

 their typical development as uninterrupted deep-sea deposits elsewhere. 



It is my belief that since the deposition of the Coal-measures the 

 Mendips, although they have been subject to oscillations of level, 

 have seldom been entirely submerged — that they formed a Carboni- 

 ferous island, which for many ages proved a barrier to the incursion 

 of the deeper-sea deposits which were taking place to the south, and 

 in which were being accumulated the materials composing many of 

 the Secondary rocks. 



Some partsof this island were the home of the Microlestes and 

 other Mammalia, and also of the Scelidosaurus (a large land rep- 

 tile discovered by myself near Shepton Mallet), which lived during 

 the Ehsetic period. Along the southern flanks of this ancient island, 

 we shall find evidences of a shallow-sea or shore deposit, and within 

 the Coal-basin itself such interruptions and thinning out of im- 

 portant geological formations as could only have occurred by the 

 interposition of a barrier like that I have referred to. Its opera- 

 tion seems to have been like that of a recent atoll, letting in only 

 here and there, or receiving on its coast-line, peculiar lithological 

 deposits, and as a consequence possessing also palaeontological differ- 

 ences, rendering it difficult to collate them with contemporaneous 

 deposits, which were at the same time being laid down under ordi- 

 nary conditions in a deeper ocean. 



5. Denudation. — Prom what has been said it must not be in- 

 ferred that there are no evidences of denudation ; on the contrary, 

 when we examine the more depressed eastern end of the Mendips, 

 in the Yallis, and in the Whatley and other combes near Erome, we 

 have abundant evidence of its operation. Throughout the whole of 

 this district the Carboniferous Limestone is highly inclined ; and it 

 follows that at the time of its upheaval it must have presented its 

 ragged edges to the surface, often no doubt running up into con- 

 siderable peaks ; but the denuding action of more recent seas seems 

 to have continued a sufficient time, and to have been powerful 

 enough, to remove these inequalities ; accordingly the upper sur- 

 faces of the edges of these upturned limestones may now be seen 

 perfectly horizontal over a considerable area. The material so re- 

 moved has served to form the various conglomerates of the district. 

 From the evidence thus afforded, and also from the peculiar way 

 in which Carboniferous Limestone fossils are found, both in the 

 Mendips and South Wales, mixed with Secondary organic remains, 

 we arrive at the conclusion that the Carboniferous Limestone has, 

 in certain areas under consideration, formed the floor of the Secon- 

 dary ocean over an enormously extended period, within which were 

 deposited elsewhere all the beds between the Oolites and the Trias, 

 and possibly even dating back to periods still more remote. 



6. System of Secondary veitis. — This view is also strengthened by 

 the fact that every vein, fissure, or depression in the Carboniferous 

 Limestone has received either horizontal deposits or infillings of 



