Horace B. Woodward — Notes an the Devonian Rocks. 447 
of migrating en masse. It certainly was not so in Palseozoic times. 
A few examples will suffice to illustrate tbis. Pentamerus galeatus, 
a species wkick, in Britain, commenced its existence in the Wenlock 
period, is not found in any American formation below tke Lower 
Helderberg group, the representative of our Ludlow. Pentamer u$ 
oblongus, wkich in the eastem 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 cliaracterized 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 kave 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 tili the Ludlow period ; the migration being obviously from 
west to east. 
Equability of climate over large areas in Palseozoic times must have 
been higkly favourable to migration. The President of the Geological 
Society, Prof. P. Martin Duncan, in his anniversary address in 
February, suggests tbat our earth is losing its atmospbere, 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 
palseontological evidence to have existed in Palseozoic 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 Bocks near Newton Abbot and 
Torquat; with Bemarks on the Subject of their Classifi- 
cation . 1 
By Horace B. Woodward, F.G.S., 
of the Geological Survey of England and Wales. 
[Eead before the British Association at Plymouth, August 16th, 1877.] 
W HEN 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 hy permission of the Director- General of the 
Geological Survey of the United Kingdom. 
