164 
DEVONIAN. 
The groupe of rocks comprising deep 
red sandstones, slates, and limestones, in 
Scotland and the marches of Wales; and 
in Devonshire exhibiting pale grey and green 
deposits, with subordiate red beds; is now 
termed the Devonian. It extends over a 
considerable portion of the slate districts of 
the globe, and in Russia alone occupies 
an extent of one hundred and fifty thousand 
square miles. These rocks are the immedi¬ 
ate predecessors of the mountain lime¬ 
stone and coal. 
Next, w^e have a second groupe of hard 
rocks, taking an inferior position, and which, 
from the district of their chief development 
in Britain, (the country of the ancient Si- 
lures,) are termed Silurian. Below the 
latter, but with questionable right to the 
honour of a separate nomenclature, lie the 
slates of the Cambrian system. As these 
however are really undistinguishable, and 
in fact zoologically identical with the lower 
Silurian, the term will probably be dropped; 
the Silurian and Devonian names will reign 
over a territory extending from the furnaces 
of the coal measures, to the peaks of the 
