1 8 The Ottawa Naturalist. [April 



were excavated. The general course of the river must have been 

 defined at an early date in the world's history, and, though since 

 that time many changes have taken place, the causes which led to 

 these may in some cases be readily seen. 



The distance from Montreal on the St. Lawrence River to 

 Georgian Bay on Lake Huron may be given as 431 miles. Of this, 

 the part between the junction ot the Ottawa and the St. Law- 

 rence at Ste. Anne and the mouth of the Mattawa is 286 miles. 

 This portion of the river has an almost direct course of fifteen 

 degrees south of east. It is, however, deflected from this course at 

 several places. Thus in the lower hundred miles it sweeps south- 

 ward around the great mass of the crystalline rocks from a point 

 a few miles above the city of Ottawa down to the mouth of the 

 River Rouge, south of which to the St. Lawrence the surface of 

 the country is generally level and occupied for the most part by 

 rocks of the fossiliferous formations or by great areas of drift sand 

 and clay. 



The portion of the river above the Mattawa may be divided 

 into two parts. From the source of the stream, which lies near 

 the heads of the Gatineau and the west branch of the St. Maurice, 

 it pursues a course a little south of west, with several large lake 

 expansions and large bends, for about 250 miles, to the head of 

 Lake Temiscaming. Here the direction of the river abruptly 

 changes. Temiscaming Lake is about sixty-one miles in length, 

 with a width diminishing from some six miles at the northern end 

 to only a few hundred yards at the southern extremity. The 

 general course of the lake and the connecting stretch of river to 

 the forks of the Mattawa, which is some thirty-five miles lower 

 down, is thirty degrees east of south. 



The drainage basin of the Ottawa is not less than 60,000 

 square miles. On the south the height of land ranges from 1,400 

 feet near the sources of the Petawawa and the Muskoka, to 417 

 feet at the divide near the head of the Rideau Lakes, while further 

 east to the north of Prescott, the height of land is within one mile 

 and a half of the St. Lawrence and the country is comparatively 

 level. Many large streams flow into the main river from either 

 side, the channels of which form deep furrows in the area which 

 they now traverse. The most easterly on the south side is the 



