ARCHEAN AND PALEOZOIC GEOGRAPHY 457 
These salt-bearing beds are succeeded by impure clayey lime- 
stone (the Waterlime). After the deposit of these beds, open-water 
conditions returned, and then a bed of limestone (the Helderberg) 
was deposited, in some places three hundred feet thick. 
Devonian Geography.— The dividing line between 
the Silurian and the Devonian is not sharp in New 
York, and there, as well as in northern Pennsylvania, 
we find the conditions of the former period extending 
by slow gradations into those of the latter. There 
is a change between the limestone of the Helderberg 
and the next higher sandstone strata (Oriskany), and 
from this to another bed of limestone (the Cornifer- 
ous). In some places these changes are abrupt, in 
others gradual. 
The next series of strata deposited in the Devonian, was one of 
sandstone and shales in the Hamilton epoch. These, as one would 
expect, are thicker and coarser in the east. Even more markedly 
is this difference in texture illustrated by the next and uppermost 
series of Devonian beds (the Portage and Chemung). The con- 
glomerate and sandstone beds existing in the Catskill region, 
mark the site of the old upper Devonian shore, along the land 
which extended eastward over New England. From this coarse 
beach the rocks grade to beds of finer grain, until in western 
New York they are sandy shales. This difference in place of ac- 
cumulation is now stamped upon the topography of the state. 
Because of the hardness of the rocks in this old beach, the Cats- 
kill Mountains stand out as bold and prominent peaks, which 
have resisted the action of post-Devonian denudation, while the 
plateaus of central and western New York, made at the same 
time, but of less durable material, have been worn down to the 
appearance of moderate irregularities. 
