498 Geological Society, 



probably feel disposed to consider the Torbay and Plymouth beds as 

 equivalent to some such rock as the old red sandstone." The au- 

 thor of the paper refrains from all reference to the memoirs of the 

 Rev. David Williams and Mr. Weaver, because his attention is more 

 particularly confined to the limestones of South Devon. In allu- 

 sion to the diversity of opinions which have been entertained respect- 

 ing these rocks, even on some occasions by the same geologist, he 

 is of opinion that it must be ascribed to the want, at the time the 

 memoirs were written, of that preponderating weight of evidence 

 which enables the mind to rest steadily on its own decisions ; and 

 that if a better result be now attainable, it must be ascribed to the 

 mass of evidence, which has been recently accumulated in various 

 parts of the kingdom. Until the organic remains of the mountain 

 limestone and Silurian system had been determined, the former over- 

 lying and the latter underlying the old red sandstone, and shown 

 by Mr. Murchison to graduate regularly into that formation, and to 

 contain perfectly distinct suites of fossils, it was impossible to de- 

 termine the age of a series of beds, the fossils of which were in part 

 new, and in part closely allied to carboniferous shells ; and procured 

 from a region but partially examined, without a base line, beset with 

 faults, and traversed by igneous rocks. 



Mr. Lonsdale then proceeds to show, what was the zoological evi- 

 dence on which he ventured in December, 1837, to conclude that the 

 South Devon limestones would prove to be of the age of the old red 

 sandstone. Previously, he had examined in part the corals of the 

 Silurian region and South Devon, and ascertained that some of the 

 species are common to both ; he had also examined with Mr. J. 

 Sowerby, Mr. Hennah's valuable collection of fossils from the neigh- 

 bourhood of Plymouth, and had become aware, from the decisions of 

 Mr. Sowerby, that certain of the shells could with difficulty, if at 

 all, be distinguished from mountain-limestone species ; and that 

 some were distinct. In December, 1837, he examined with Mr. 

 Austen a portion of that gentleman's collection of Newton Bushell 

 fossils, and though he ventured to differ from some of the identifi- 

 cations with mountain-limestone species pointed out to him, yet 

 these shells agreed so much in aspect with testacea of the carboni- 

 ferous fauna, that he could not doubt there was a connexion between 

 the beds from which they had been obtained and the mountain lime- 

 stone system : the same collection also proved that, associated with 

 these shells were corals of Silurian species. He had also been in- 

 formed by Mr. Austen, that in beds connected with the limestone, 

 the Calceola sandalina had been found. It was therefore by com- 

 bining the amount of the above evidence, the presence in the same 

 strata of shells, identical, or nearly identical, with mountain-limestone 

 species, of Silurian corals, the Calceola sandalina, and a numerous 

 distinct testacea, that he suggested the South Devon limestones 

 would prove to be of an age intermediate between the carboniferous 

 and Silurian systems, and consequently of that of the old red sand- 

 stone. In alluding to Professor Sedgwick and Mr. Murchison's 

 adoption of the suggestion in 1839, and their bold application of it 



