Murchison’s Siluria. 375 
senting to the public a volume which should not be too strictly 
scientific to interest any but the professional geologist, and which, 
at the same time, might not, like the works previously mentioned, 
be inaccessible to many on account of its great cost. For this 
purpose, the original plates of fossils drawn by Mr. Sowerby 
and engraved for the “ Silurian System” have been reproduced 
by transferring to stone, with the exception of the corals, which 
being originally lithographs could not be thus made use of again. 
These latter however have been, with additions and corrections, 
drawn upon wood, and numerous species are also figured in this 
way which have been found in Great Britain’since the “ Silurian 
System” was published, or of which better specimens have been 
obtained ; these were drawn on wood by Mr. Salter. . Thus the 
and invaded by igneous masses, and hence so complicated in their 
stratigraphical relations, and moreover so poorly supplied with 
fossils, that it has required all the skill of the government corps 
Manner, to determine the structure of the region nee, 
hile Murchison had sichite Ga his views and divided the Silu- 
tian rocks into a number of groups, which have, in the main, 
been recognised by the Government Geological Survey, and, 
_ _ What is of still higher importance, had caused the typical organic 
forms of his system to be described and figured, thus enabling 
