THE GEOLOGICAL HISTORY OF NEW YORK STATE TOT 
igneous activity in general. By this means materials are brought 
up from within the earth to or near its surface. Thus an active 
volcano violently ejects rock fragments, dust etc. or more quietly 
pours out molten rock, while in many cases great masses of molten 
rocks have been forced upward into the crust of the earth without 
reaching the surface and hence have slowly cooled at greater or 
lesser depths below the surface. Such volcanic rocks have become 
exposed to view only by subsequent erosion of the region. 
In order to understand the physical history of our State it is 
necessary to know that significant changes, like those above 
described, have long been, and now are taking place. In tracing 
this history we shall see how all these natural processes have 
operated to bring the State into its present condition. It is also 
necessary to understand that the known history of the earth has 
been carefully divided into great eras, and into lesser periods and 
epochs, and that these constitute what is called the geologic time 
scale. This time scale is important to the reader because the prin- 
cipal events in the history of the State will be taken up, so far as 
they are recorded, in regular order according to that scale. In the 
first table the names of eras and periods are mostly of world-wide 
usage, while the names of subdivisions (epochs) of the periods are 
much more local in usage and, in the second table, only those are 
given which apply to New York State. 
GEOLOGIC TIME SCALE 
ERAS PERIODS DOMINANT LIFE 
Quaternary Age of man 
Cenozoic 
Tertiary Age of mammals 
Age of reptiles, with birds first in 
M : Cretacic the Jurassic, and trees and flowers 
eSOZOIC | ; ; 
Jurassic of modern aspect first in the Cre- 
J tacic 
Triassic Age of amphibians, with cycad plants 
(Ge enERIC } common 
| Carbonic Great coal age, with large nonflower- 
ing plants 
Paleozoic Devonic Age of fishes 
Cambric simple fishes in the Siluric 
Proterozoic Algonkic 
Archeozoic Archean 
Earliest known forms of life 
Siluric 
Le A | ee 
L Ontonicn ge of invertebrates, with some very 
i but records very imperfect 
