Page:Popular Science Monthly Volume 68.djvu/208

 204 in these easily recognized and contrasted strata are of great significance when taken as illuminating the more obscure relations of the Precambrians of the interior mountains.

One interesting corollary of the great northeast and southwest breaks is that a series of basaltic dikes which are widely distributed, which followed the metamorphism of the Precambrian rocks, but which preceded the Potsdam, almost always come up through them and suggest that the breaks go far enough down to have tapped off a reservoir of basic rocks.

The Drainage.—The waters from the Adirondacks flow into both the Hudson and the St. Lawrence Rivers. On the south and southwest they either go directly to the former which rises in their very center;



or else they pass first through the Mohawk. On the north and east, the waters reach the St. Lawrence viâ Lakes George and Champlain, and on the northwest viâ Lake Ontario or directly to the great river itself. The drainage of the high mountains, however, goes almost entirely to the Hudson or to Lake Champlain.

The chief rivers actually in the area are the Hudson and its principal tributary north of Waterford, the Sacondaga, both of which will be shortly described in greater detail; West Canada Creek, and minor tributaries of the Mohawk; the Black, flowing into Lake Ontario; the Oswegatchie, Grass, Raquette, and Salmon-Chateaugay, which pass directly into the St. Lawrence; and the Saranac, Ausable and the outlet of