632 
THE FRESH-WATER LOCHS OF SCOTLAND 
Lesser Slave Lake is a shallow lake, 60 miles long, with an average 
breadth of 8 miles, draining by the Lesser Slave River into the 
Athabasca River. It covers an area of about 480 square miles, and is 
mostly less than 10 feet deep. 
Lake Athabasca (or Lake of the Hills), 690 feet above sea-level, 
is 195 miles long, by 35 miles in maximum breadth, and has an area 
of about 3000 square miles. No soundings have been made in the lake. 
Great Slave Lake is 391 feet above sea-level, and is 300 miles 
in length, by about 50 miles in breadth. Its area is about 10,000 
square miles. No soundings have been made in the lake. 
Great Bear Lake, 340 feet above sea-level, is 175 miles long, has 
an area of 11,200 square miles, and is very irregular in shape. The 
average depth is 270 feet. 
River Abundant proof is furnished of the existence of the Mississippi 
Mississippi, j^i^gj, previous to the glacial epoch by the change that occurs in its 
valley where the southern limit of the ice invasion intersects its course, 
between the junctions with the Missouri and with the Ohio. South 
of the glacial boundary the Mississippi flows through an ancient valley 
which has been filled with alluvium to a depth of one or two hundred 
feet in its northern part, and to an increasing depth southward. 
North of the boundary the course of the river is through a narrow, 
steep-sided valley, and is interrupted by many rapids alternating with 
places, in the driftless area of Wisconsin and Minnesota, where the 
valley broadens and displays signs of old age. The waters of the 
great tributary of the Mississippi, the Missouri, are supplied in part 
by the hot springs and wonderful geysers of the Yellowstone Park, 
where the Yellowstone River drains the lake of the same name. 
Yellowstone Lake, 7788 feet above sea-level, is about 20 miles 
in length, by 10 to 15 miles in breadth, the circumference being about 
100 miles, and has an area of about 150 square miles. In some places 
it is said to be over 300 feet in depth, while the average depth is about 
30 feet. It was "in blossom'' when I visited it in September 1907, 
the whole surface being at that time covered with masses of green 
oscillatoriae. Near the point of exit of the Y^ellowstone from the lake, 
at its north end, is a belt of hot springs 3 miles long by ^ mile wide, 
some of them extending into the lake. 
Two-Ocean Pond is a small lake a few miles south of Yellowstone 
liake. It is on the summit of the range — on the great continental 
divide — and has two outlets : one into the Atlantic through the 
Yellowstone and Missouri Rivers, the other into the Pacific through 
the Snake River, a branch of the Columbia. 
Lake Mendota, in Wisconsin, lies 846 feet above sea-level, and is 
15 square miles in area and 84 feet in maximum depth. The town of 
