212 Prof. J. W. Spencer — High Continental Etc ration. 



breadth of the submerged valley throughout its windings for a 

 length of 800 miles or more, is remarkably regular, only gradually 

 increasing its magnitude in passing seaward. Other lesser channels 

 are visible in the soundings ; thus south of the Straits of Canso, 

 between Nova Scotia and Cape Breton Island, there is one 1200 feet 

 deep, where adjacent soundings show less than 600 feet of water. 



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

 the channel is 1200 feet deep. This depth increases in passing 

 down the Straits, where the scanty soundings show 2040 feet, before 

 reaching the mouth. Here, in Hudson Straits, the old valley is 

 a chasm across a mountain system, whose peaks, upon the southern 

 side, rise to 6000 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 in- 

 scribed 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 Missis- 

 sippi canon. The lake-basins are all excavated out of Palaeozoic 

 rocks, except a part of that of Lake Superior. 



The soundings do not afford all the infoi'mation that we desire, 

 yet they demonstrate the presence of submarine valleys reaching 

 upon all our coasts to depths of more than 3000 feet. Again, the 

 soundings show that to within comparatively short distances from 

 their mouths, the depths of the valleys below the surface of the 

 seas sometimes did not exceed from 1200 to 1S00 feet, but that 

 beyond there was a great increase in depth within the last few 

 leagues. 



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

 by terrestrial crust movements, yet the leaving open of great yawn- 

 ing chasms is not of sufficiently well-known occurrence to attribute 

 all the submerged valleys upon the American coasts to such an 

 origin, especially when we consider the great length of the sub- 

 merged channel of the St. Lawrence Eiver (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 

 hill-sides. These, together with other meteoric agents, have also to 

 a greater or less extent removed the Palaeozoic and the Triassic 



