CHAPTER II. 



GENESIS OF LAKE LAHONTAN. 

 THE FORMATION OF LACUSTRAL BASINS. 



The discussion of the origin of lake basins has been carried on with 

 so much zeal during the past fifteen or twenty years that we now possess a 

 large amount of literature bearing on the subject. From the facts gathered 

 by many observers, in widely separated localities, it is evident that the de- 

 j)ressions holding lakes are extremely diverse in character and have resulted 

 from many causes. In some instances lakes are held in basins produced by 

 orographic movement, i. e., by the unequal folding of rocks, by dislocation 

 due to faulting, etc. Others are the result of erosion, and have for their 

 typical example a rock-basin produced by glacial action. Again, there is a 

 third great group of basins produced by the damming of pre-existing water- 

 ways; as, for example, when the drainage of a valley is obstructed by 

 moraines, land-slides, lava-flows, alluvial deposits, etc. 



Following the schedule prepared by Davis, ^^ we have three broad 

 classes of lake basins : 



a. Constructive or orographic basins. 



b. Destructive or erosion basins. 



c. Obstructive, barrier, or inclosure basins. 



Each of these generic divisions is abundantly illustrated in the Great 

 Basin. Very large portions, if not the entire area of interior drainage, have 



'» Classification of Lake Basius, by W. M. Davis ; Proceedings of the Boston Society of Natural 

 History, Vol. XXI, 1882, p. 321. 



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