LAKES OF NORTH AMERICA, 



CHAPTER I. 



ORIGIN OF LAKE BASINS.^ 



Difficulties arise in classifying- lake basins, similar in character to 

 those met Avith when a systematic discussion of glaciers, rivers, mountains 

 and other features of the earth's surface is attempted. That is, there are 

 no natural groups separated by hard and fast lines, into which they 

 ]iaturally fall. Certain types ma}- be selected, however, answering to 

 genera among plants and animals, about which most lakes may be 

 grouped. In selecting these t3q)es we are guided Ity tlieir mode of origin, 

 and are thus led to an incom})lete genetic classification, based on the 

 natural agencies Avhich produce depressions in the earth's surface. 



Depressions on new land area. — On lands recently elevated above 

 the sea or left exposed by the evaporation or drainage of inland water bodies, 

 tliere are usually ineciualities, and water frecpiently collects in the (le})res- 

 sions and forms lakes. There are comparatively few lakes of this type in 

 North .Vmerica, for the reason that large portions of our coasts are sinking 

 and new land areas are rare. The lakes of Florida, however, are good 

 exam[)les of this class. They are surrounded l)y marine rocks of recent 

 oiigin. and aie but slightly elevated above the sea. In fact, all of the 

 toi)ogra|)hic features of Florida indicate immaturity. The luxuriant 

 vegetation of the southeastern coastal [)lain, masks the slight inequalities 

 of the surface, and. by clogging tlic slack drainage, leads to a greater 



1 This subject has been diseussed l)y muiicnuis writers, ami lias led to eontroversies imt 

 yet ended. "The most extended and most systematic treatment that it has received may 

 be found in an essay l)y \V. M. Davis "On the classification of lake basins," in Boston 

 Soc. Nat. Hist., I'roc., vol. 21, 1882, pp. .'1 1 •')-:]« 1 . The numerous references sriven in this 

 paper constitute the best bil)lioLM-ai)liy nf the subject available. An important .supplementary 

 jiapcr by the same author is rcpublishiMl as an appendix of tlu' present volume. 



