﻿Horace B. Woodward— Notes on the Devonian Hocks. 447 



of migrating en masse. It certainly was not so in Palaeozoic times. 

 A few examples will sufSce to illustrate this. Fentamerus galeatus, 

 a species which, in Britain, commenced its existence in the Wenlock 

 period, is not found in any American formation below the Lower 

 Helderberg group, the representative of our Ludlow, Fentamerus 

 oblongus, which in the eastern hemisphere and in eastern North 

 America is not found higher than the Clinton group (our May Hill 

 Sandstone), ascends into the Niagara (Wenlock) formation in more 

 westerly localities. A more striking example may be cited. Our 

 Ludlow rocks are characterized by an abundant Lamellibranchiate 

 fauna, notably by the genera Pterinea, Goniophora, and Cypricardinia. 

 In North America, this fauna is represented, not in Silurian, but in 

 Middle Devonian (Hamilton) rocks, by forms which, in some cases, 

 are specifically identical, and, taken as a whole, are strikingly 

 similar. We are bound to regard the Hamilton as true Devonian, 

 since it lies above strata with a distinctively Devonian facies, and far 

 above formations which clearly represent our Upper Silurian groups. 

 In all these cases, the migration must have been from east to west. 

 On the other hand, the Merostomata flourished in the Water-lime 

 formation (Upper Wenlock) in the west; but in the east they do not 

 appear till the Ludlow period ; the migration being obviously from 

 west to east. 



Equability of climate over large areas in Paleozoic times must have 

 been highly favourable to migration. The President of the Geological 

 Society, Prof. P. Martin Duncan, in his anniversary address in 

 February, suggests that our earth is losing its atmosphere, as the 

 moon has already lost hers ; and, consequently, our atmosphere 

 must have been denser in earlier periods. This would probably 

 account for the greater equability of climate which we infer on 

 palgeontological evidence to have existed in Palaeozoic epochs. If, 

 then, migrations were wider and more rapid in ancient periods, 

 fossils must be even better tests of contemporaneity than in younger 

 formations. 



VI. — Notes on the Devonian Eocks near Newton Abbot and 

 Torquay; with Eemarks on the Subject of their Classifi- 

 cation.^ 



By Horace B. "Woodward, F.G.S., 

 of the Geological Survey of England and Wales. 



[Read before the British Association at Plymouth, August 16th, 1877.] 



WHEN we consider the growth of geological knowledge in our 

 own country, we soon learn how very detailed must be the 

 character of all new work compared with that performed by the great 

 pioneers in the science. Much that has now to be done may be 

 called the microscopic work, labour that is often uninteresting and 

 dry, except to the individual himself, but which nevertheless is most 

 useful and necessary. 



The more or less rapid traverses of the earlier geologists enabled 



1 This paper is communicated by permission of the Director- General of the 

 Geological Survey of the United Kingdom. 



