ROCKS OF SCOTLAND. 335 
those of the Silurians of Canada and the United States, but 
that some of its organisms not yet found in England seem to 
be even identical with those of the other side of the Atlantic. 
It contains a terebratula indistinguishable from a Canadian 
species, and a Maclurea determined by M’Coy to be the Mac- 
lurea magna of the United States. This last massive genus, 
which resembles that of Euomphalus, save that its whorls lie 
in nearly the same plane, is by no means rare in the limestones 
of the Girvan district, but so much so in the Silurians of the 
sister kingdom, that it does not appear in Murchison’s great 
work. Some of our graptolites are also identical, it is said, 
with American species; and, on lately exhibiting my small 
collection of Scoto-Silurian fossils to a geologist of the United 
States, he told me that none of the organisms which he had 
yet seen in the museums of our country so reminded him, 
from their general appearance, of those of his own. It is 
surely not uninteresting thus to find the hitherto little known 
Silurian deposits of Scotland connecting its geology, by links 
not elsewhere found in Britain with the geology of Bohemia 
on the one hand, and with that of the New World on the other. 
I need searee add, that our Old Red Sandstone, in its Holopty- 
chii and Asterolepi, furnishes similar links that connect it with 
the Old Red Sandstones of Russia and the American colonies. 
Both systems,—though deemed, at a comparatively recent 
time, so poor in the organic, that in the one, according to Hut- 
ton, “geologists alleged there was not to be found any vestige 
of organized body,” and that in the other, according to Mur- 
chison, geologists contended there were no organisms, at least 
peculiar to it as a deposit, are now recognized as not only 
important depositories of the geologic records of the country, 
that fill up vast periods in its physical history which would 
have otherwise remained unsatisfactory blanks, but as also 
establishing, by their remains, the identity of its character, in 
