44 THE POPULAR SCIENCE MONTHLY. 



marvelous fact of lake distribution. Prof. Bonney passes it by 

 with the remark that there is a perfect gradation of lakes from 

 the smallest tarns to those of North America and Central Africa ; 

 and Mr. Douglas Freshfield says that wherever on the surface 

 of our globe there are heights there must be hollows ; and other 

 writers think that lakes are general results of the process of 

 mountain-making. But none of these writers have apparently 

 even noticed the fact that glacier valley lakes have a distinctive 

 character which separates them broadly from the lakes of all 

 non-glaciated countries, and that they are totally absent from 

 such countries. 



But besides the mountains which possess true valley lakes, 

 there are a number of ranges which have been glaciated yet do 

 not possess them, and this absence of lakes has been used as an 

 argument against the connection of valley lakes with glaciation. 

 A little examination, however, shows us that these cases greatly 

 strengthen our argument. Comparatively large and deep valley 

 lakes are the result of excessive glaciation, which has occurred 

 only when conditions of latitude, altitude, and moisture combined 

 to produce it. In regions where glaciation was of diminished in- 

 tensity, from whatever causes, valley lakes diminish in size and 

 number, till at last only tarns are found in moderately glaciated 

 districts. Thus, the Pyrenees were far less severely glaciated 

 than the Alps ; they consequently possess no large valley lakes, 

 but numerous small high lakes and tarns. As we go eastward in 

 the Alps, the diminished rain and snowfall led to less severe gla- 

 ciation, and we find the valley lakes diminish in size and numbers 

 till far east we have only tarns. The Carpathians have no valley 

 lakes, but many tarns. The Caucasus has no lakes and very few 

 tarns, and this may be partly due to the steepness of the valleys, 

 a feature which is, as we shall see, unfavorable to lake formation. 

 In the South Island of New Zealand the lakes are small in the 

 north, but increase in size and number as we go south where the 

 glaciation was more intense. These numerous facts, derived from 

 a survey of the chief mountains of the world, are amply suffi- 

 cient to show that there must be some causal connection between 

 glaciation and these special types of lakes. What the connection 

 is we shall inquire later on. 



THE CONDITIONS THAT FAVOR THE PRODUCTION OF LAKES BY 

 ICE EROSION. Those who oppose the production of lake basins by 

 ice erosion often argue as if the size of the glacier was the only 

 factor and urge that, because there are no lake basins in one val- 

 ley where large glaciers have been at work, those which exist in 

 another valley where the glaciers were no larger, could not have 

 been produced by them. But this by no means follows, because 

 the production of a lake basin depends on a combination of 



