GEOLOGY. 241 



heavy pressure ; and, jud^in^ by such a basis, it could not have 

 been less than 10,U00 years that the coast of Maine was under im- 

 mense icebergs, and undergoing the change which it now presents. 

 In certain parts of Maine, and extending even into Canada, large 

 holes are found which were evidently formed by this same pres- 

 sure, just previous to the decline of the drift period, and in the 

 commencement of the glacial period. 



LAKE BASINS. 



_ Prof. Newberry, at the 1868 meeting of the American Associa- 

 tion, presented an abstract of a paper on "The Surface Geoloo-y 

 of the Basin of the Great Lakes and the Upper ^Mississippi Valley!" 

 He hoped to give some information which would aid in working 

 out the great problem of the drift. The drift formation has been 

 investigated most generally from the top downward. Tliis prod- 

 uct of the glacial period in this region has not received sufficient 

 attention. Fragments of limestone from islands in Lake Superior 

 show glacial scratches. Sometimes the furrow is very deep, — ef- 

 fects commonly produced by glacial action. This is the proper 

 source of the drift formation ; upon this different kinds of material 

 rest. Boulders are found 500 miles from their native I'ocks. Some- 

 times the clay is fine and stratified, and again it contains gravel 

 and some boulders ; above this is a bed of bouldi-rs and gravel, 

 which is the glacial moraine. The valleys of the rivers were ex- 

 cavated by the glaciers to a depth far below their present level. 

 Sometimes shafts are sunk 150 feet before these beds are reached. 

 There was doubtless once a river-connection between Lakes Erie 

 and Ontario. Lake Erie was formerly only a river, — the ancient 

 river-beds in the vicinity being from 100 to 150 feet below the 

 present level of the streams. At Louisville there was an apparent 

 exception, as there were rock-bottoms in the river, but the city 

 occupies the site of the ancient river-bed. Sometimes there are 

 tw'o bluff formations of different ages. All this clearly indicates 

 that formerly the country was more perfectly drained ; that is, that 

 the continent was more elevated. When these valleys were ex- 

 cavated, the drainage was free to the ocean, similar to the condi- 

 tion in California ; and the rivers, by their great erosion, wearing 

 awav the hard rocks. The orig-in of the Niao^ara and Hudson 

 Rivers was evidently glacial. The ancient beds of the rivers on 

 the Pacific coast were far below their present level, showing great 

 land elevation. It is not certain that the continental elevation was 

 sufficient to afford a temperature essential to the formation of the 

 glaciers, which were afterwards melted and left the material of 

 the drift. The glaciers were not unbroken, so that some varieties 

 of formation are found. No glacial action can account for the cop- 

 per and granite formations, but there is no other reasonable theory 

 concerning the boulders found in the region of the lakes. 

 21 



