DEPOSITS IN 'IKE BRISTOL DISTRICT. 



81 



remarked, the peculiar circumstances attending their discovery has 

 always left this in some obscurity. They are now assigned by 

 Mr. Etheridge to the Dolomitic Conglomerates at the base of 

 the Keuper. These conglomerates are in great part composed of 

 rounded boulders of the Carboniferous Limestone, some of them of 

 great size, and seemingly requiring glacial conditions for their 

 removal and transportation. Not only do they fringe the outcrops 

 of the limestone from which they are derived, but they form an 

 almost continuous deposit of considerable thickness, extending for 

 many square miles in the Somersetshire coal-basin, the inclined 

 ragged limestone edges of which are, in places, rendered by their 

 denudation quite horizontal. The removal and redeposition of the 

 conglomerates indicate very troublous times, during which it seems 

 impossible for any organic life to have existed ; for nothing could 

 have withstood the grinding-processes to which it would have been 

 subjected ; and it is a significant fact that no organic remains have 

 ever been referred to this period except the reptilians under notice. 



Eor these reasons, and from my having found the teeth of The- 

 codontosaurus and Palceosaurus in the B-hsetic deposit at Holwell, 

 and also from my subsequent discovery of the Khgetic bone-bed and 

 remains of that age almost alongside the Clifton reptilia, I had 

 come to the conclusion that the latter belonged to this period — a 

 view which further investigation respecting both Keuper and Ehaetic 

 reptilia requires me to modify. Seventeen Thecodont teeth, more or 

 less perfect, are in my Holwell series. On comparison with those 

 from Bristol, they are more robust, have a more wrinkled or 

 striated surface, with the serrations on the edges smaller, less 

 oblique, and more numerous. In my paper " On Abnormal Con- 

 ditions " &c.*, I gave a section of variegated Keuper marls at 

 Euishton, near Taunton, one bed of which I described as a " Gritty 

 conglomerate, with occasional sandy bands and intermediate layers 

 of marl, with fish, reptile, and batrachian remains, fourteen inches 

 thick." In this bed I have lately found some teeth of Thecodonto- 

 saurus, which appear in all respects identical, in form, structure, 

 and the character of the serrations on their edges, with those from 

 Bristol. It contains also Acrodus Jceuperinus, .Hybodus, Diplcdus, 

 &c. It is rather a coarse sandy bed than a conglomerate ; and, owing 

 to its being rather unconsolidated, its remains are very fragile. 

 There seems little doubt that this bed is on the horizon of that in 

 Warwickshire which has yielded identical vertebrata; and if so, the 

 Bristol reptilia will have to be removed one stage later in time, from 

 the Dolomitic Conglomerate to the middle of the Upper Keuper. 



It is an interesting palgeontological fact that, although most of 

 the generic forms of the Keuper recur in the Rhsetic beds, so far as 

 I have ascertained, the species differ, and are special to the two 

 formations. 



* Quart. Journ. Geol. Soc. vol. xxiii. (1867), p. 468. 



Q. J. G. S. No. 145. 



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