Page:Popular Science Monthly Volume 15.djvu/329

 ; 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 precipitates 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 evaporation below its outlet, 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 corresponding 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, without 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