II) 
and Geographical geology, although minerals and other economic 
products are slightly represented and will be increased as collec- 
tions are obtained. 
Geological Names. — During the early study of the geological 
formations, it became necessary to apply names to the different 
beds and groups of beds, in order to classify them and study 
their relations to each other and to those of other countries. 
This gave rise to a geological nomenclature, which is based 
partly on the organic remains {fossils) found in the rocks, and 
partly upon the localities where studied or where best developed : 
and a few have reference to the nature of the rock itself. The 
first series of names is that of Epochs, and serves to designate 
small groups of strata of limited extent, characterized by peculiar 
species of fossils confined within the epoch. These epochs are 
grouped under Periods which have a wider signification, both in 
time, in the geographical distribution of the rock, and in their 
fossil contents. The next larger grouping is under Ages. These 
are named from the prevailing type of life existing within their 
limits, as the Age of Reptiles, Age of Mammals, &c. The largest 
grouping has reference to the times of the earth's history and the 
forms of life represented, as Eozoic time, or time of the dawn of 
life, &c. The names of epochs and periods below the Carbonifer- 
ous age, are those adopted by the New York geologists during 
the survey of the state, and are those most generally used in this 
country. Many of the others are of European origin. 
The accompanying tabular section, Fig. i* (copied from Dana's 
Manual of Geology, with a few changes only), illustrates the- geo- 
logical nomenclature and classification. The succession, as given 
under the Reptilian age, is mostly European, the American rocks 
of these periods not being fully understood at present. The 
horizontal section, Fig. 2, is an ideal one from Northern New York 
to Pennsylvania, showing the succession and superposition of the 
formations in New York. 
•A very large proportion of the cuts used in this Guide are taken from Dana's Manual of 
Geology, the author and publishers of which very kindly furnished electrotypes, at the cost of 
production, for this use. Otheis are copied front various works. 
