THE GEOLOGICAL HISTORY OF NEW YORK STATE 25 
and into Westchester county. The relief is rather rugged with the 
higher points commonly reaching altitudes of over 1000 feet. The 
rocks are chiefly granites and gneisses of Precambric age, and are 
in most ways much like those of the Adirondacks. 
Region north of the Highlands. North of the Highlands the 
rocks are in the main highly metamorphosed shales, sandstones and 
limestones, and the relief is generally low except along the eastern 
border where it is almost mountainous. A characteristic feature 
along this eastern side is the presence of long, fairly high, nearly 
north-south ridges separated by comparatively narrow valleys. 
Shawangunk mountain. Lying close to the southeastern border 
of the Catskills and extending northeastward from the State line 
in Orange county well into Ulster county, is a distinct mountain 
ridge known as Shawangunk mountain. This long, narrow moun- 
tain rises 1000 feet or more above the surrounding country, and 
with the deep narrow Rondout valley immediately on its west side 
and the broad, open Wallkill valley on the east, it is truly a re- 
markable topographic form. The capping of very hard Siluric 
conglomerate upon the soft Ordovicic shales has caused the ridge 
to stand out so boldly against erosion (see figure 9 and plate 28). 
Region south of the Highlands. Southern Rockland county is 
covered by Mesozoic (Triassic) sandstone. This rock is not folded 
but contains within its mass great sheets of lava which outcrop to 
form the Palisades along and west of the Hudson (see figure 20). 
In southern Westchester county and in New York county there 
are highly folded and metamorphosed Precambric and Ordovicic 
rocks, and the country is typically hilly. 
LONG ISLAND PROVINCE 
This province, including Staten Island, is really a part of the 
broad Atlantic coastal plain and is therefore practically devoid of 
any hard rock formations at the surface. Except for a few ex- 
posures of Cretacic sands and gravels along the northern border, 
the whole province is made up of glacial sands and gravels. From 
the standpoint of surface relief the province is clearly divisible into 
two parts, a northern and a southern, which are sharply separated 
from each other (see plate 12). The northern part is character- 
istically hilly, the hills being of glacial (morainic) origin. The 
maximum elevation is less than 400 feet, while in general the hills 
are from 100 to 200 feet high. This line of hills ends abruptly 
about midway of the island (north-south) and the southern part of 
the province is a sand plain of remarkable smoothness with a gentle 
slope toward the ocean. 
