12 
THE UEOLOGIST. 
Professor Sedgwick, in the same paper, recognizes the Plymouth 
gi'oup in the slates of Looe, Polperro, and Fowey, in Cornwall.* 
Accepting, at least provisionally, this clironology, we have, when 
considered chronologically as well as geographically, what, as a mat- 
ter of convenience, may be called five fossiliferous areas ; namely, a 
deposit of the age of the Plymouth group in each of the districts, 
South Devon, North Devon, and Cornwall ; and one of the Barn- 
staple age in each of the two latter. To avoid repetition, they will 
be spoken of throughout this paper as Lower South Devon, Lower 
North Devon, Lower Cornwall, Upper North Devon, and Upper 
Cornwall. The terms "Upper" and " Lower" are to be understood 
as applied relatively to the rocks of Devon and Cornwall only, and 
not as embodying or implying any opinion respecting the co-ordina- 
tion of these rocks with deposits of the Devonian age elsewhere. 
Had existing materials warranted, it wonld have been desirable to 
have made a further division, namely, one having reference to the 
mineral character of the deposits, as well as to time and place; for it 
is certain, as might have been expected, that in the same area some 
fossils are peculiar to the argillaceous beds, and others are found 
only in the calcareous strata; thus, for example, I learn from Mr. 
Godwin-Austen that he has found the remarkable coral Fleuro- 
dictyum prohlematicum in the slates, but not in the limestones, at 
Ogwell, in South Devon. My own experience is in harmony with 
this. 1 have found specimens of the same fossil in the slates at Tor- 
quay, and hundreds of them occur in rocks of the same character at 
Looe, in Cornwall, but not a trace of it in limestone anywhere. 
The two species of sponges belonging to the genus Stegano diet yum 
of Professor M'Coy occur in the slates along the entire coast of 
Cornwall, from Powey Harbour to the Kame Head ; at Bedruthen 
Steps in the north of the same county ; and at Mudstone Bay, near 
Brixham. in South Devon; but have never been met with in cal- 
careous strata. At present, however, it would be premature to at- 
tempt a division of this kind. 
My present object is to give some account of the amount and 
character of the Devonian population of the five areas as above 
defined, when the census was last taken. The inquiry as to cha- 
racter goes no further than to ascertain to what extent they were a 
migratory or colonizing race. 
HaA'ing spent a considerable portion of the leisure I have been 
able to command during the last twenty years in collecting and 
studying the fossils of the districts under consideration, especially 
along the entire line of coast extending from Polperro in Cornwall 
to Torbay in Devonshire, and also at South Petherwin, I have natu- 
rally been led to pay some attention to their distribution in time 
and space ; and several concurring circumstances have recently 
brought the subjects more prominently before me. Amongst other 
things I may mention a passage in the recent address of Professor 
* Quai'tci'lv Journal Geol. Soc. vol. riii. p. 11. 
