THE GEOLOGICAL HISTORY OF NEW YORK STATE 23 
rather flows across a broad, low, hilly region of very moderate 
relief thus allowing the low rocky hills to stand out as islands. 
The rocks are chiefly sandstones and limestones of Cambric and 
Ordovicic ages, though, in the vicinity of the Thousand Islands 
numerous patches of the underlying Precambric (Adirondack) 
rocks are exposed as on many of the islands themselves. Folds, 
faults and igneous rock are not present except in the Precambric 
rocks, and the strata may be regarded as a comparatively thin 
mantle of nearly horizontal layers overlying the Precambric rocks. 
CHAMPLAIN VALLEY PROVINCE 
The Champlain valley bounds the Adirondacks on the east and 
the province should be regarded as a great depression separating the 
Adirondacks on the west from the Green mountains on the east. 
Much of the valley bottom is filled by the waters of Lake Cham- 
plain (elevation 101 feet). Along the western shores of the lake 
the topography is characteristically hilly, though seldom above 500 
feet in elevation. The transition to the higher and rugged Adiron- 
dacks is generally rapid. 
The rocks occupying the valley bottom are sandstones, limestones 
and shales of Cambric and Ordovicic ages. These formations are 
much disturbed by numerous faults, often of considerable magni- 
tude, and in fact there is good reason to think that the whole 
Champlain valley is of the nature of a great fault-trough or 
depression. 
HUDSON VALLEY PROVINCE 
General description. Looked upon in a broad way, the Hudson 
valley province is a depression lying between the western high- 
lands of New England and the eastern highlands of New York. 
Well toward the south the true valley feature is somewhat inter- 
fered with by the presence of such elevated masses as Shawangunk 
mountain and the Highlands-of-the-Hudson. A very detailed 
classification of topographic features would call for four or five 
provinces instead of the one here called the Hudson valley province. 
Since even this southern part, however, is lowland compared with 
the Catskill mountains immediately westward and since the rock 
structures are so similar and characteristic throughout the region, 
though the kinds of rocks vary considerably, it seems best for our 
purpose to treat all together as the Hudson valley province and 
then very briefly describe each of the minor subdivisions of the 
province. 
