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Siluria—Present State of Geology. 317 
sions of the Silurian System. Sir Roderick has established 
his Silurian system with uncontrovertible evidence in Great 
Britain and Ireland, Germany, France, Belgium, North 
America, Spain, Portugal, Sardinia, Cape of Good Hope, 
Himalaya Mountains, Hindostan, Australia, South America, 
United States, Falkland Islands, &c. 
We now give several extracts from the concluding remarks 
of Sir Roderick’s work, written in a highly popular and gra- 
phic style, and we are sure that our general readers will not 
only be much delighted, but edified, with what follows, and 
hope it will induce many to study the work. 
*“« Passing rapidly over the earliest stages of the planet, which are 
necessarily involved in obscurity, our sketch of ancient nature began 
with the first attainable evidences of the formation of sediments com- 
posed of mud, sand, and pebbles. It was shown that the lowest 
accessible of these deposits, though of enormous dimensions, and 
occasionally less altered than strata formed after them, are almost 
entirely .azozc, or void of traces of inhabitants of the seas in which 
they were accumulated. One solitary genus of zoophytes has been 
alone detected in most bottom rocks, the heat of the surface during 
these earlier periods having been, it is supposed, adverse to life. 
“* Proofs were then adduced to demonstrate that in the next for- 
mations, scarcely differing at all in mineral character from those 
which preceded them, observers in various regions had detected clear 
and unmistakable signs of a contemporaneous appearance of animal 
life, as shown by the presence of a few genera of crustaceous mol- 
lusks and zoophytes, occupying layers of similar date in the crust of 
the earth. Proceeding upwards from this protozoic zone, wherein 
organic remains are comparatively rare, we then ascended to other 
sediments, in which, throughout nearly all latitudes, we recongise a 
copious distribution of submarine creatures, resembling each other 
very nearly, though imbedded in rocks now separated by wide seas, 
and often raised up to the summits of high mountains. Examining 
all the strata exposed to view that were formed during the first long 
natural epoch of similar life termed Silurian, we found that the suc- 
cessive deposits were charged with a great variety of forms—of the 
trilobite, a peculiar crustacean—of the orthoceratite, the earliest 
chambered shell—as well as with numerous exquisitely formed mol- 
lusks, crinoids, and zoophytes; the genus graptolite, of the latter 
class, being exclusively found in these Silurian rocks. In short, my 
contemporaries have assembled from those ancient and now desic- 
cated marine sediments, or repositories of principal creatures, ex- 
amples of every group of purely aquatic animals, save fishes. The 
multiplied researches of the last twenty years have failed to detect 
