80 PALiEONTQLOQY OP 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 iii, 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- 



