210 



II. A host of them are distributed in northern United States and Canada, 

 including the greatest collection of fresh waters on the globe. 



III. A good number in the Sierra Nevada and the Rocky Mountains. 



The remainder of the country from the southern boundary of Georgia to the 

 northern boundary of Pennsylvania west to the Rockies is practically free from 

 lakes, except 



IV. along either side of the lower Mississippi and Red Rivers. 



These four groups of lakes are due to four different methods of lake forma- 

 tion, but all four are indicative of the fact that the lake-rich areas have under- 

 gone recent change. 



The first series is due to the comparatively recent elevation of an irregular 

 ocean floor. The second series is due to the action of ice in the irregular gouging 

 and irregular dumping of debris. These are all of recent date, probably none of 

 them being over 10,000 years old. The third series is due to the exigencies of 

 mountain formations, including in this plication and plication hollows, craters 

 and lava flows and the settling of small areas. The fourth is due to the change 

 of channel on the part of the Mississippi and to the debris brought down by the 

 Red River which it has deposited at the mouths of its tributaries.* 



Of course the lakes of one of these regions need not be all of the same origin. 

 Small lakelets around Lake Tahoe in the Sierra Nevada are certainly due to the 

 gouging action of glaciers coming from a steep incline onto a comparatively level 

 plain. Generally speaking, mountain regions, unless, as in the case of the 

 Appalachian, they have outgrown their lake stage, contain lakes of the greatest 

 diversity of origin. 



Lakes are of interest to the geologist to determine the particular way in 

 which a general cause has been modified to produce a particular efl^ect at any 

 particular lake; to the physicist to account for the various colors, temperatures, 

 pressures, reflections, refractions, etc.; to the chemist to determine the degree of 

 concentration of minerals and gases in solution ; they are of interest to the 

 naturalist to determine the organic inhabitants, their quantity and kind and 

 their life histories; to the cecologist and evolutionist to determine the geological, 

 physical and chemical characters in their eff'ect on the organic inhabitants and 

 these on each other. 



Lakes may therefore be studied for other than purely economic interests, 

 such as water supplies and liighways for commerce or location of summer resorts. 



■•'The facts for the foregoing have largely been drawn from Russell's American Lakes. 

 Ginn & Co., 1895. 



