PROFOUND DEPTHS OP LAKES AND RIVERS. 69 



British Admiralty charts, while adjacent soundings show less than 600 feet 

 of water. 



Hudson's Bay rarely exceeds a depth of 600 feet, yet at the outlet the 

 channel is 1,200 feet deep. This depth increases in passing down the straits, 

 where the scanty soundings show 2,040 feet before reaching the mouth. 

 Here, in Hudson's Straits, the old valley is a chasm across a mountain sys- 

 tem, whose peaks, upon the southern side rise to 6,000 feet above tide. The 

 canon of the St. Lawrence also crosses the trend of two mountain systems? 

 but these are of no great height. The same is not true for any of the other 

 submarine valleys described. 



The record of a former high continental elevation is again inscribed in 

 the depths of the Great Lakes — Ontario reaching to 491 feet below ocean 

 level, Superior to nearly as much, Michigan to 300, and Huron to 150 feet. 

 The lake basins are merely closed up portions of the ancient St. Lawrence 

 valley and its tributaries. Their distance from the sea would necessitate not 

 merely a general elevation of the continent, but also a greater amount of 

 elevation towards the head-waters of the system, as has been shown with 

 regard to the excavation of the upper portion of the ancient Mississippi 

 canon. The lake basins are all excavated out of Paleozoic rocks, except a 

 part of that of Lake Superior. 



The soundings do not afford all the information that we desire, yet 

 they demonstrate the presence of submarine valleys reaching upon all our 

 coasts to depths of 3,000 feet or more. Again, the soundings show that 

 within comparatively short distances from their mouths the depth of the 

 valleys, below the surface of the seas, sometimes did not exceed from 1,200 

 to 1,800 feet, but that beyond, there was a greater increase in depth, within 

 the last few leagues. 



Whilst depressions in the earth's surface are made and modified by terres- 

 trial crust movements, yet the leaving open of great yawning chasms is not of 

 sufficiently well known occurrence to attribute all of the submerged valleys 

 upon the American coasts to such an origin, especially when we consider the 

 great length of the submerged channel of the St. Lawrence river (800 miles), 

 its various windings, and its uniformly increasing size, until it passes into 

 the great chasm, just before it reaches the margin of the continent. The 

 idea of the excavation of these submerged valleys by glaciers — some of which 

 are outside of glacial regions even of the past — is too untenable for a moment 

 of serious consideration. Irrespective of the causes which have determined 

 the location of the channels here described, it appears that they have been 

 made one and all by the excavating power of rivers and lateral streams 

 pouring down the hillsides. These, together with the other meteoric agents, 

 have also to a greater or less extent removed the Paleozoic, and also the 

 Triassic rocks, from the depressions now occupied by the Gulfs of St. 



