GEOLOGICAL SURVEY OF FORTIETH PARALLEL. 315 



tan ; it occupied western Nevada with an area nearly equal to that of 

 Lake Bonneville, but more broken with islands and promontories. It 

 is now represented by Pyramid, Carson, and Walker's Lakes. 



These two Quaternary lakes were, of course, the products of ages 

 during which the precipitation of moisture in the Great Basin was 

 much larger than now ; but Mr. King states that the complete history 

 of the climatic changes in this region during the Quaternary included 

 two moist periods with a dry interval between them, and that these 

 have been succeeded by another interval of aridity, that of the present. 

 Gilbert had previously shown that a period of dryness had preceded 

 the moist period in which Lake Bonneville was filled ; and Mr. King's 

 study of Lake La Hontan indicates another period of humidity which 

 preceded that. The reasoning by which he reaches this conclusion is 

 extremely ingenious, and is based upon the varying chemical precipi- 

 tates from the waters of Lake La Hontan. In past times the waters 

 which drained into this lake were highly charged with carbonate of 

 soda, and during periods when the lake-waters were concentrated by 

 evaporation, Gaylussite, the hydrated double carbonate of lime and 

 soda, was deposited in sheets on its sides. At other times, when the 

 volume of water was greater, the soda was dissolved out, and carbonate 

 of lime alone precipitated in pseudomorphs after Gaylussite. From 

 facts of this character, which we have not space to present in full, he 

 feels warranted in stating 1. That the lake was formed in a period 

 of abundant precipitation, and had free drainage to the ocean ; 2. In 

 a period of desiccation, the level of the lake was reduced by evapora- 

 tion below its qutlet, and the saline contents concentrated to the point 

 of formation of Gaylussite ; 3. The coming on of a second flood- 

 period which filled the basin to its point of overflow, when the soluble 

 salts were all washed out and the pseudomorph thinolite was formed ; 

 4. A modern rapid desiccation which nearly emptied the lake-basin, 

 leaving only a few small, weakly saline lakes as its representatives. 

 Mr. King connects these periods of greater precipitation with two corre- 

 sponding periods of glacial extension, and from these facts hints rather 

 than asserts that elsewhere, as well as there, superabundant moisture 

 was the cause of glacial extension, and therefore of those records which 

 are generally regarded as proofs of a cold period. A discussion of the 

 phenomena and causes of the " Ice period " would be incompatible 

 with the limitations of this paper, but we may say in passing that the 

 generalization which has been suggested by Mr. King seems hardly 

 warranted by the facts he reports. It is certainly true that there could 

 be no formation of ice or glaciers, however low the temperature, with- 

 out precipitated moisture, and in many places the extension of glaciers 

 is limited not by temperature, but by lack of moisture ; but, to find 

 standards of comparison with the widespread glaciers of the Ice period, 

 we must go to the Arctic and Antarctic Continents. Here we are far 

 removed from the theatre of most active evaporation, and where the 



