80 
PALEONTOLOGY OF NEW-YORK. 
of igneous matter are accompanied by formations of rapid accumula¬ 
tion. 
Following the evidences from the oldest geological times, we find in 
the later periods a greater accumulation of trappean or volcanic pro¬ 
ducts, which in many instances have added largely to the mass of the 
sedimentary deposits with which they are associated, or of themselves 
have produced extensive masses. 
Volcanoes proper, and their products, are of modern date ; and it has 
been shown by the observations of numerous geologists, that these 
phenomena are always associated with the tertiary or more modern 
geological formations. I believe that these phenomena have been pro¬ 
duced in regions of great and rapid accumulation of other deposits, and 
can never occur except as the result of such conditions. These igneous 
outflows, therefore, I regard as produced by and dependent upon other 
agencies, and are but the manifestations of rapid accumulations of 
sedimentary matter. 
It is thus at the termination of the series, and where may probably 
exist the entire sequence of formations, that we find the greatest exhi¬ 
bition of volcanic phenomena in any geological period. 
Therefore it would appear that we have, in the slower accumulations, 
the highest mountain chains produced in the most recent geological 
periods ; while the results of later accumulations, under other circum¬ 
stances, have given us the stupendous volcanic phenomena which have 
been manifested from the earliest tertiary epochs. 
In the present introduction to Volume in, it was not originally my 
intention to extend this discussion to formations beyond those which 
constitute a part of the great system, the fauna of which I have en¬ 
deavored to illustrate in its sequence, and to some extent in its geo¬ 
graphical distribution. I have, however, necessarily been drawn into the 
discussion of certain principles applicable to all geological formations 
of whatever period, and which are indeed elementary as well as fun¬ 
damental to the science. Instead of stating these views simply as con- 
