STUDY OF THEM INDISPENSABLE. Ill 
Other families, both of animals and vegetables, 
are limited to particular formations, there being 
certain points where entire groups ceased to 
exist, and were replaced by others of a different 
character. The changes of genera and species 
are still more frequent ; hence, it has been well 
observed, that to attempt an investigation of 
the structure and revolutions of the earth, with- 
out applying minute attention to the evidences 
afforded by organic remains, would be no less 
absurd than to undertake to write the history 
of any ancient people, without reference to the 
documents afforded by their medals and inscrip- 
tions, their monuments, and the ruins of their 
cities and temples. The study of Zoology and 
Botany has therefore 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 different, but even in 
the same formations,* that similarity of mineral 
composition is but an uncertain proof of con- 
temporaneous origin, while the surest test of 
* The same formation which in England constitutes the argil- 
laceous deposits of the London Clay, presents at Paris the sand 
and freestone of the Calcaire Grossier ; whilst the resemblance 
of their Organic remains, proves the period of their deposition 
to have been the same, notwithstanding the difference in the 
character of their mineral ingredients. 
