882 The American Naturalist. [October, 
economic and mineral resources of the respective States, these 
surveys necessarily became concerned with other work. It 
was soon found that in order to intelligently describe the rocky 
strata, it was essential to give the rocks distinct names. These 
were, at first, taken from mineralogical characters, and such 
terms as “ metalliferous” and “ geodiferous limerock ” were the 
result. Or the name was given from some special physical 
aspect, and then “cliff limestone” and “ marlite” were ap- 
plied. Finally, however, the plan of giving the formations 
the names of localities where the rocks were either best devel- 
oped or had been first observed was adopted, and then such 
names as “ Potsdam,” “ Trenton ” and “ Niagara ” were used. 
Another matter, too, which soon became one of the promi- 
nent features of the geologists’ work, was the study of the 
organic contents of the rocks. It was early observed that cer- 
tain species occurred constantly in certain strata, while above 
or below them, other and different species were found. When 
once this fact was established, geologists availed themselves of 
it to place in one horizon, or to consider as of one age, the beds 
containing the same species of fossils, even when found in dis- 
tant parts of the country. 
The lack of any method of coöperation between the mem- 
bers of the various State surveys, led to great diversity of 
nomenclature. In New Jersey, Pennsylvania and Virginia, 
the formations were known by numbers; in Ohio and Indiana 
they received names from lithological features, while in New 
York it early became the plan to give the various formations 
names of places where they were best exposed. Perhaps it is 
to be considered fortunate for the science that so many of the 
State surveys ceased early, else the nomenclature might have 
been as varied as the different States had rocks. It was the 
vitality or persistence of the New York Survey that enabled 
her geologists to establish a system of names for almost the 
whole North American Continent, so far, at least, as the rocks 
lying within her borders were capable of doing. Thus the 
“ New York System” became a standard to which was referred 
strata of similar character occurring in all parts of the coun- 
try. 
