On the Chronological Value of the Triassic Strata of the South-western Counties

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Abstract
I n no part of the south-western counties is a more detailed section of the Triassic rocks exhibited than on the South-Devon coast. It is the district in which the subdivisions seem to have attained their maximum thickness; and though they may be traced in unbroken conformity to Williton, near the shores of the Bristol Channel, the absence of the lower members of the group to the east of Taunton, and a study of the variable relations of land and water during the period in different parts of the area, render the proof of the following propositions a necessary supplement or second part of the paper which I have already had the honour of communicating to the Society*. F irst P roposition .—That the South-Devon and West-Somerset Triassic area was not connected with that of Gloucester and the midland counties till the later stages of the Keuper period. Proof. —(a) The tailing-off of Triassic. sediments towards the Mendip country. (b) The representation of the Trias on the north of the Poldens by marls alone, the Dolomitic conglomerate being a contemporary beach. (c) The abnormal thinning-out of the Trias on the north of the Mendips. Thus at Tyning pit, near Radstock†, it was bottomed at 186 feet; at Norton-Hill pit at 172 feet; at Batheaston (under Rhætic) at 54 feet ; in Mangotsfield cutting at 25 feet. The general results arrived at by Mr. Moore give an average thickness of 50 feet to the Trias within the coal-basin. (d) The fact that these marls, being in

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