376 Murchison’s Siluria. 
geologists in other parts of the world to identify rocks of the 
same age, Sedgwick had made but little progress in his district, 
and certainly had not published a sufficiently clear account of his 
ambrian rocks and their fossil contents to enable geologists to 
recognise them as forming a distinct system. The name Silurian 
has therefore been almost universally adopted; and when it was 
found that Sedgwick’s Cambrian was nothing more nor less than 
Lower Silurian, the latter name had already become too familiar 
to make it possible, had it been desirable, to exchange it for an- 
other. Murchison did, indeed, on the authority of Sedgwick, 
for a time admit that the Cambrian rocks were distinct from and 
lower than his Lower Silurian; but he soon became convinced 
that this was an error, as has since been proved by the government 
geologists, who have demonstrated that the supposed lower rocks 
of North Wales are physically and palzeontologically identical 
with the groups of Siluria. Unfortunately, as we think, the name 
of Cambrian has been retained by the British Geological Survey 
and is now applied to the non-fossiliferous rocks, below an arbi- 
trary base line, in which no fossils have as yet been found. The 
sandstones of Barmouth and Harlech, the slates of Llanberis and 
the conglomerates, grits and schists of Longmynd are included 
in the Cambrian as at present understood. These rocks, however, 
are not unconformable with the fossiltferous beds lying directly 
over them, and if hereafter, they should be found to contain or- 
ganic remains and these should be Lower Silurian types, then the 
name of Cambrian would have to be dropped. 
The whole space occupied in England and Wales by rocks 
supposed to be azoic is very small, only a few patches being col- 
ored as Cambrian on the geological map accompanying our au- 
thor’s work ; and should any or all of these beds prove to contain 
a few traces of organic life, it need not excite surprise, or at 
invalidate our belief in the existence of a system of sedimentary 
beds destitute of organic remains in other parts of the world. 
Geologists have, indeed, been generally unwilling to admit that 
in the Lower Silurian we have reached the lowest zone of organic 
ory that in the lowest Silurian strata we have the first represent 
atives of organized existence, that we are justified in asserting 
that a base line may be drawn from which paleontologieal rea 
soni “Russia and the Ural Mountains” 
soning may start. In his “ 2 U | 
1845) he thus expresses himself: “On this point, we have te 
