502 THE GLACIAL LAKE AGASSIZ. 



eastern coast from IMaine to Labrador and Greenland, and our western 

 coast from Puget Sound to the Arctic Ocean, was eroded by a stream that 

 flowed along- the bottom of the gorge when it was above the sea; and this 

 erosion was probably going forward in the epoch immediately preceding 

 the Ice age, for earlier subsidence during any period of much length, 

 geologically speaking, would liave caused the submerged valle)^ to be filled 

 with sediments. The preglacial elevation of the Saguenay region therefore 

 appears to have been at least about 1,000 feet greater than now. 



Similarly it is proved by the fjords of Maine, the eastei'u Canadian 

 provinces, and Newfoundland, of Labrador and Greenland, of the Arctic 

 coasts of North America, and the archipelago west of Baffin Bay, and of 

 the Pacific coast from Alaska to Oregon, that the entire extent of the 

 North American glaciated area was considerably higher before than after 

 glaciation. 



But the preglacial altitude of this area was much greater than the 

 depth of the fjords which indent its shores. It is more nearly, but proba- 

 bly still only partially, measured by river valleys and fjords which are now 

 entirely submerged beneath the ocean. The submarine border of the con- 

 tinental plateau to depths of more than 3,000 feet is cut by valleys or 

 channels which if raised above the sea-level would be fjords or canyons. 

 These can be no other than river courses eroded while the land stood much 

 higher than now; and its subsidence evidently took place in a late geologic 

 period, else the deposition of silt must have obliterated the channels. For 

 this continent a most impressive review of the evidences of its lately far 

 greater height, as shown by these submerged river courses, has been given 

 by Prof. J. W. Spencer.' 



According to the United States Coast Survey charts, as noted by 

 Spencer, the bottom of a submerged valley just outside the delta of the 

 Mississippi is found by soundings at the depth of 3,000 feet. This valley 

 is a few miles wide and is bounded by a plain of the, sea bed from 900 to 

 1,200 feet above its floor. It thus appears that the country north of the 

 Gulf of Mexico has been raised for a short time to a height of not less than 



>"The high eoiitineutal elevation preceding the Pleistocene period, " Bulletin, G. S. A., Vol. I, 

 1890, pp. 65-70 ; also m the Geol. Magazine (3), Vol. VII, pp. 208-213, May, 1890. 



