282 
ition or graywacke and carboniferous series; Mr. Prideaux being 
the only author who ascribes them in part, and on mineral characters, 
to the old red sandstone; and Mr. J. Phillips, in his article on geo- 
logy in the Encyclopedia Metropolitana, hesitating to place them 
in a definite position, in consequence of the resemblance of many of 
the shells to species found in the mountain limestone. Mr. De la 
Beche, in his memoir on Tor and Babacomb Bays, also states that 
the limestones of that district rest on old red sandstone; and in his 
Report on Cornwall and Devonshire (1839), he says, “‘ that those 
who rely very exclusively on the character of organic remains would 
prohably 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 
Rey. 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. Bushel 
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 wasa 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- 
