kelatiox of lakk8 to climatic conditions. 57 



Types of Fresh Lakes. 



Of the tens of thousands of fresli lakes scattered over North America, 

 and especially abundant in the previously' glaciated, northeastern por- 

 tion of the continent, or forming a p,art of the more impressive scenery 

 of the C'ordilleran region, many might be selected as types. Atten- 

 tion .will be confined, however, to the Great Lakes, drained by the St. 

 Lawrence, Lake Tahoe, California, and Lake Chelan in the State of 

 Washington. 



The Laiiroiitian lakes. — The group of great lakes drained by the 

 St. Lawrence, as is well known, contain the most magnificent examples 

 of fresh water-bodies now existing on the earth. I^ake Superior still 

 retains its position as the largest sheet of fresh water known, although 

 tlie moi-e recent discovery of Lake Victoria Xyanza has brought a rival 

 into the field. This African lake is estimated to have an area of about 

 18,000 square miles, which is 12,000 square miles less than the area of 

 tlie great American lake ; but when an actual survey shall have been 

 made, it is possible that this difference will be materially decreased. 



AVhile Lake Superior exceeds all other fresh lakes in extent, it ranks 

 second among terrestrial water-bodies, for the reason that the Caspian 

 Sea is the largest sheet of water not in open communication with the 

 ocean, mnx existing. The Caspian is saline, however, and falls in the 

 second great division of lakes here recognized. 



The origin of the basins of the Laurentian lakes has been referred to 

 in Chapter L in connection with the action of glacial agencies in obstruct- 

 ing drainage ; an account of their jjast history is given in advance in dis- 

 cussing the Pleistocene lakes of the same region ; at present attention 

 Mill be confined to some of the more interesting features of the existing 

 lakes. 



The U. S. Lake Survey. — A survey of the Laurentian lakes was 

 made by the Corps of Engineers, U. S. Army, l)etween 1841 and LS81, 

 and is known as tlic V. S. Lake Survey.^ On the ina[)s or cliart ])ul)lis]u'(l 

 by that survey, the outlines of the shores of the lakes and of their con- 

 necting waters are given, together, with the topography of a narrow stri[) 

 of the adjacent land ; the de[)th of water, character of bottom, etc.. as 



1 Ivtlinrt uiMiii tlic Primary Triangulatiuu of tliL' U. S. Lake Survej', by Lieut. -Cdl. ('. 15 

 Couistoelc. Wasliiim^toii. ]S«2. 



