TOSSIL GEOLOGY OF UNITED STATES. 291 
surd than to undertake to write the history of any 
' ancient people without reference to the documents 
afforded by their medals and inscriptions, their 
monuments, and the ruins of their cities and tem- 
ples. The study of zoology and botany has, there- 
fore, become as indispensable to the progress of 
geology as a knowledge of mineralogy. Indeed, 
the mineral character of the inorganic matter of 
which the earth's strata are composed, presents so 
similar a succession of beds of sandstone, clay, 
and limestone, repeated irregularly, not only in dif- 
ferent, but even in the same formations, that sim- 
ilarity of mineral composition is but an uncertain 
proof of contemporaneous origin, while the surest 
test of the identity of time is afforded by the corre- 
spondence of the organic remains : in fact, without 
these, the proofs of the lapse of such long periods 
as geology shows to have been occupied in the for- 
mation of the strata of the earth, would have been 
comparatively few and indecisive. The secrets of 
nature that are revealed to us by the history of fos- 
sil organic remains, form perhaps the most stri- 
king results at which we arrive from the study of ge- 
ology. It must appear almost incredible to those 
who have not minutely attended to natural phenom- 
ena, that the microscopic examination of a mass of 
rude and lifeless limestone should often disclose the 
curious fact that large proportions of its substance 
have once been found parts of living bodies. It is 
surprising to consider that the walls of our houses 
are sometimes composed of little else than com- 
minuted shells, that were once the domicil of other 
animals at the bottom of ancient seas or lakes. 
It is marvellous that mankind should have gone on 
for so many centuries in ignorance of the fact, 
which is now so fully demonstrated, that no small 
part of the present surface of the earth is derived 
from the remains of animals that constituted the 
population of ancient seas. Many extensive plains 
