TRIASSJC STRATA OF THE SOUTH-WESTERN COUNTIES. 465 



This remarkable similarity, coupled with the presence of quartzite 

 fragments in the Keuper conglomerates of the midland counties, 

 though by no means proving a continuity of the areas, shows that 

 similar conditions prevailed synchronously and independently in 

 early Keuper times in the midland and south-western counties. 



Organic Remains. — Fossils have not been discovered in the Trias 

 of either area under comparison below the Keuper Sandstones, 

 whilst remains of the same genus have been found in the Upper * 

 and Lower t Keuper Sandstones in each ; for it is no stretch of 

 imagination to regard the sandstone-beds of Claverham, near Yalton, 

 of North Curry and Ruishton &c, as equivalent to the Upper Keuper 

 Sandstone, bearing in mind the irregular mode of occurrence of that 

 stratum %. 



As regards thickness, I have allowed a maximum of 1350 feet to 

 the Upper Marls of the south coast of Devon §, but should be sur- 

 prised to find the division exceed 1000 feet in Taunton Yale, the 

 Bridgewater or Polden-Hill districts. It seems probable that Mr. 

 Moore's jj estimate of 2000 feet for the average thickness of the Trias 

 outside the coal-basin embraces the whole formation in the Bridge- 

 water district, if not meant to include the areas of Devon and West 

 Somerset. At any rate the average thickness of 50 feet assigned to 

 the Trias of the Mendip area, and the probability of its attenuation 

 in Taunton Yale, would load one to regard a thickness of from 700 to 

 800 feet a fair estimate for the Keuper Marls to the north of the 

 Blackdown range, as they have not been fathomed at 609 feet in the 

 boring at Compton Dundon^f. 



Professor Hull** gives the following comparative thickness of the 

 marl in the midland counties : — in Lancashire and Cheshire, 3000 

 feet ; in Staffordshire, 800 feet ; in Leicestershire, 700 feet. 



He gives the following comparative thickness of Lower Keuper 

 Sandstone : — in Lancashire and Cheshire, 450 feet ; in Staffordshire, 

 200 feet ; in Leicestershire and Warwickshire, 150 feet. 



I have assigned 530 feet as the maximum thickness of the Upper 

 Sandstones of Devon ; but I am inclined to think that they seldom 

 exceed from 400 to 450 feet, and may not attain to 200 feet in the 

 Watchet valley or Bridgewater district. 



It is very doubtful whether they extend far eastwards below the 

 marls in the vale of Taunton, and rather probable that the area 

 between the Mendip and Poldens was dry land during their depo- 

 sition. If the pebble-bed and conglomerate subdivision be added, a 

 total thickness of from 300 to 550 feet might be assigned to the 

 Upper-Sandstone division in Devon and West Somerset. 



(c) From the foregoing considerations I have no hesitation in 



* Mem. Geol. Surv. on Triassic &c. pp. 5, 120 ; comp. Quart. Journ. Geol. 

 Soc. vol. xxiii. p. 468. 



t Op. cit. p. 120; comp. Quart. Journ. Geol. Soc. for May 1869, p. 152, &r\, 

 and vol. xxxii. p. 274. 



\ Mem. Geol. Surv. op. cit. p. 96. 



§ Quart. Journ. Geol. Soc. vol. xxxii. p. 380. 



f Ibid. vol. xxxii. p. 381. % Bid. vol. xxiii. p. 458. 



** Mem. Geol. Sur. op. cit. p. 108. 



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