2 
PALAEOZOIC CLASSIFICATION OF THE BRITISH ISLES. 
in Devonshire, the whole reposing upon ancient grauwacke masses, which, how- 
ever poor in calcareous matter and fossils, apparently represented a portion of the 
Silurian system of the British Isles. The proofs of this German succession are 
to be found in the 6th volume of the Transactions of the Geological Society of 
London 1 ; the chief geological inductions of the English authors, Professor Sedg- 
wick and Mr. Murchison, are there sustained by an elaborate analysis of the De- 
vonian organic remains by M. de Verneuil and Vicomte d’Archiac. 
But although the classification of these ancient formations was thus in great part 
established, the questions of what is the protozoic type, and whether a distinct and 
peculiar assemblage of fossils could be discovered in rocks of higher antiquity 
than the Lower Silurian, had not yet been completely grappled with, — questions, 
indeed, not even approached by the investigations in any part of Germany. In 
short, it still remained to inquire whether the older Cambrian slates were so cha- 
racterized, and whether they were entitled to be considered a separate zoological 
system ? And here it is right to acquaint geologists who may have misapprehended 
its meaning, that the term Cambrian was applied by Professor Sedgwick to the 
great slaty and partially fossiliferous group of North Wales, the chief relations of 
which he defined as early as 1833, distinguishing it from an upper group in 
Denbighshire. Unfortunately ill health and other circumstances prevented his 
examining and describing the fossils he had collected, and thus the types of the 
lower rocks of North Wales were unknown when the Silurian divisions were pro- 
posed and established. At that time, indeed, Professor Sedgwick believed, and in 
this opinion Mr. Mui’chison coincided, that when developed, these Cambrian organic 
remains, at least all the lower part of them, would prove to be distinct from the 
Lower Silurian types, which as a whole seemed to repose upon the slaty and cry- 
stalline rocks of North Wales. When this division was first suggested, it was, 
however, shown, that many of the most common fossils of the Lower Silurian type 
descended into the so-called Cambrian rocks. Speaking of the Orthidce, Lepteence 
and other shells which had even then been found in the latter, Mr. Murchison 
said, “ As these shells abound in the Lower Silurian rocks, it would seem that as 
yet no defined line of zoological division can be drawn between the Lower Silurian 
and Upper Cambrian groups, and that as our knowledge extends we may probablv 
fix the lower limit of the Silurian system beneath the line of demarcation which has 
for the present been assumed.” And further, the same opinion is more strongly 
1 pp. 221 et scq. 
