igoi] Ells — Ancient Channels. 19 



South Nation which rises near the St. Lawrence not far from the 

 town of Brockville, and after a somewhat tortuous course of 100 

 miles reaches the Ottawa about forty miles east of Ottawa city. 

 The descent of the river in this distance is not more than 100 feet, 

 so that, allowing- for the High Falls near Casselman and several 

 rapids between that place and the Ottawa, it will be seen that for 

 the greater part of its course the waters of the South Nation must 

 be comparatively sluggish. 



The elevation of the height of land to the north which divides 

 the waters of the Ottawa from those flowing into James' Bay is 

 rarely more than 1,000 feet above sea-level. Over a large part of 

 this area to the north, embracing many thousands of square miles 

 in this direction, the surface is covered with heavy deposits of sand 

 which overlie thick beds of clay. These deposits extend from the 

 lower Ottawa and the St. Lawrence nearly, or in places quite, to 

 the height of land. In the absence of fossils in these higher clays 

 positive evidence of their marine origin cannot be obtained, but it 

 may be stated that they are continuous northward with those 

 which do contain such organisms, and therefore the assumption 

 may be made that the sea, at some date prior to or at the time of 

 their deposition, had invaded all the northern country to a depth 

 • of some hundreds of feet. 



The denudation of the old crystalline rocks, which were the 

 first to appear throughout this area, must have been enormous. 

 How many thousands of feet have thus been removed, cannot be 

 surmised. But along portions of the lower Ottawa, as in the 

 stretch below the Joachims Rapids, known as the Deep River, 

 the present bottom of the channel is now many feet below the sea- 

 level, the surface of the river being about 370 feet above tide, while 

 soundings made several years ago are reported to have reached 

 a depth of over 500 feet. 



In Lake Temiscaming also, certain portions have been 

 sounded and show that here the excavation has been very great. 

 At one point a depth of 470 feet was obtained, while the surface of 

 the lake is 591 feet above the sea. There must therefore have 

 been a large amount of denudation throughout this part of the old 

 river basin, though certain parts of this old channel have 

 since been to a certain extent tilled in by glacial deposits. 



