GEOLOGICAL HISTORY OF NEW YORK. 655 



the Coast Survey, to be distinctly marked upon the sea-bottom out to a 

 point some eighty miles southeast of New York, and where the water is 

 now over 500 feet deep. Here we reach the true margin of the conti- 

 nent, where the shore plunges rapidly down into the depths of the 

 ocean ; and here was for ages the mouth of the Hudson River ; for the 

 channel which leads to it could not possibly have been excavated except 

 upon a land-surface. 



2. Explorations made over a large part of the territory lying be- 

 tween the Atlantic and the Mississippi show that many of the drain- 

 ing streams are now flowing far above their ancient beds, and that these 

 sometimes lie below the present ocean-level. For example, the Ohio 

 flows in a valley the bottom of which is occupied by sand and gravel 

 at least 100 feet thick. The rock -bottoms of the streams which empty 

 into the Great Lakes are at their mouths sometimes 200 feet below the 

 water-level. The Mohawk Valley is filled to a great depth with loose 

 materials, the surface of which forms for long distances a nearly level 

 plain, through which the present river meanders. 



Innumerable instances of this kind could be cited, all of which go to 

 prove that for ages the eastern half, at least, of this continent stood 500 

 to 600 feet higher above the ocean than now, and that during this time 

 the draining streams with swiftly-flowing currents cut the surface into 

 a network of deep channels not unlike the canons of some of the rivers 

 of the far West. 



There seems to be good reasons for believing also that in this 

 period of elevation the stream which drains the basin of the Great 

 Lakes, called in different parts of its course the St. Mary's, the Detroit, 

 the Niagara, and the St. Lawrence, flowed not through the modern 

 channel, which passes the Thousand Islands and the Lachine Rapids, 

 but, leaving the basin of Lake Ontario at its southeastern corner, trav- 

 ersed the now deeply-buried channel of the Mohawk, and entered the 

 present valley of the Hudson somewhere near Albany precisely where 

 has not 3'et been determined, as heavy beds of drift cover and conceal 

 its course for many miles in that vicinity. From Albany this ancient 

 Hudson River flowed through a deeper and wilder valley than the 

 present one, which is half filled with water, passed what is now New 

 York Island, far below the present water-surface, was joined at the 

 Battery by a large tributary from the east, issued from the highlands 

 by a picturesque gate at the Narrows, and, traversing a littoral plain, 

 emptied into the ocean eighty miles southeast from New York. 



The limits of this article will not permit the presentation of all the 

 facts which sustain this view, but a few of them will suffice to show 

 that it hardly admits of doubt. These are briefly as follows : 



An ancient connected line of drainage passes through the basin of 

 the Great Lakes at least 200 feet below the present water-surface, deep- 

 ening eastward, and reaching a level much below that of the bed of 

 the St. Lawrence. 



