230 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



(2.) According to this view of the subject, the older Palaeozoic 

 rocks of Britain will be brought into a good accordance with the 

 Palaeozoic sequence in Bohemia and North America ; and such good 

 observers as Hall and Barrande will be relieved from a very great diffi- 

 culty in comparing their magnificent older Faunas vnth that of England 

 and Wales. It may be true (as indicated in the works of Professor Hall) 

 that the separation betwen the upper and lower divisions of the older 

 Palaeozoic rocks of America is more sharply defined than in England ; 

 and we know M. Barrande allows hardly any interchange of species 

 between his upper and lower di\'isions of the older Bohemian rocks. 

 Hence these two authors may have been led to suppose that the 

 development of the older Palaeozoic rocks in England was imperfect 

 or anomalous. I believe, however, that this Paper will help to clear 

 up any such misconception ; for it exposes one unexpected source of 

 confusion, and helps us to separate our Cambrian and Silurian groups 

 more completely than they were ever separated before*. 



(3.) There is so wide a distinction between the collective organic 

 types of the Primary (or palaeozoic) and Secondary periods, that we 

 may conveniently regard them as exhibitions of two distinct systemata 

 naturae. But the same cannot be said of the great subdivisions, 

 such as the Carboniferous, Devonian, and Silurian series, &c. These 

 subdi\-isions are sometimes ill-defined, and have certain species in 

 common. The Carboniferous fauna at its inferior limit may be par- 

 tially confounded with the Devonian ; and in like manner the Devo- 

 nian with the upper portion of the Silurian, and the Silurian vrith the 

 upper portion of the Cambrian. Hence it might be better to use the 

 word Series rather than System, as applied to these palaeozoic sub- 

 divisions. It is, indeed, a matter of comparatively small moment by 

 what names they are described, provided our conventional terms be 

 well-defined and understood ; but this we may, I think, venture to 

 affirm — that if we adopt the word 'system' in the more limited sense 

 in which it has during late years passed current in the Geological 

 Society, the Silurian and Cambrian systems are as well separated, 

 both physically and palaeontologically, as any of the so-called systems 

 of the great Palaeozoic series. 



* The Palaeontological separation between the Cambrian and Silurian rocks is, 

 I believe, still more complete in Westmoreland and Cumberland than it is in 

 Wales and the counties adjacent to it. This will be evident to any one who will 

 take the trouble of analysing the lists given in the 2nd Fasciculus of the Cam- 

 bridge fossils above referred to. A less perfect list of fossils (collected in the 

 northern counties) was given by Mr. Salter as an appendix to a second edition of 

 Four Letters by myself on the Geology of the Lake District, published in 1846. 

 His first list contains more than 120 species derived from the series of beds above 

 the Coniston limestone group. His second list, from the Coniston group, contains 

 about seventy species. Larnellibranchiata abound in the first list, and are not 

 found in the second ; and very few species (not more than two or three) are 

 common to his two lists. 



