E^SUMfi OF PHYSICAL HISTORY. 171 



lithoid terrace and the Lahontan beach remains to be considered in con- 

 nection with the chemical study of the lake. 



The great number of" water-lines scoring the interior of the Lahontan 

 basin shows that the main changes in the history of the lake were accom- 

 panied by many minor fluctuations. The absence of an outlet renders it 

 evident that the minor oscillations as well as the more permanent horizons 

 recorded b)' the ancient terraces were due to climatic changes, the nature 

 of which will be considered in a future chapter. 



From this brief resume it will be seen that the facts in the physical 

 history of the lake can be correlated but imperfectly, yet give evidence 

 that they have a definite sequence and are in fact fragments of a connected 

 history. In the chemical studies which follow we shall be able to present 

 some of the pages that are here missing and sketch the history of Lake 

 Lahontan with greater completeness. 



