FOSSIL 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 



