12 GEOLOGY OF OHIO. 



* 



action of this agent was directly antagonistic to that of local glaciers. 

 That the New England ice-sheet was of great thickness is proved by the 

 continuity of the furrows made by it, up hill and d6wn dale ; showing 

 that these irregularities of surface, though considerable, were slight 

 when compared with the thickness of the ice-mass above them. Mount 

 Washington serves as a kind of Nilometer to the glacier, and proves its 

 upper surface to have been 6,000 feet above the level of the sea ; in 

 other words, that the ice was 3,000 feet thick. Dana has estimated that 

 at its place of origin, on the watershed between the St. Lawrence and 

 Hudson's Bay, the thickness of the ice-sheet was 11,500 feet; but there 

 is little doubt that the watershed was higher then than now, and hence 

 the thickness of the ice may have been less than estimated. 



BURIED CHANNELS. 



Intimately connected with the glacial markings, and in part produced 

 by the same cause, are the great number of deeply excavated, now 

 buried, channels, which have already been briefly noticed. Some of 

 these channels may have been, in part, formed long anterior to the ice 

 period, as all the area of the Eastern, Middle, and North-western States • 

 has been a land surface, traversed by drainage lines, since the close of the 

 Carboniferous period. We may, therefore, conclude that many of our great 

 arteries of aqtieous circulation have been in action all through the Meso- 

 zoic and Tertiary ages. My attention was first called to these ancient 

 water-courses by the facts brought to light in the borings for petroleum, 

 so actively prosecuted in the valleys of our western rivers in 1860-61. 

 In this enterprise I had both pecuniary and scientific interests, by 

 which I Was led to visit all the centers of oil production in the country > 

 and in all I found some traces of deeply excavated, and now partially 

 filled, valleys and ravines, of which I could, at first, give no explanation. 

 When the observations made in different localities were combined, how- 

 ever, they revealed the existence of a connected system of drainage 

 lying at a lower level than that now in action, and one that could only 

 have been excavated in a long interval of time, and when the continent 

 stood at a much higher level than now. Some of the facts to which I 

 have referred, and the conclusions to which they led, were given by the 

 writer in a paper on the Surface Geology of the Basin of the Great Lakes', 

 published in the Proceedings of the Boston Natural History Society', 

 May, 1862. In this paper these interesting phenomena were first brought 

 to the notice of American geologists. Since that time a fuller exposi- 

 tion of the subject has been presented in the Annals of the Lyceum of 

 Natural History, New York, June, 1869, and in the Report of Progress 



