552 A TREATISE ON METAMORPHISM. 



streams flow, some of them of considerable size, for instance, the Bear, 

 Ogden, and Weber rivers. The smaller streams which flow into the basin 

 for the most part rise on the mountain slopes of the Wasatch and Sierra 

 Nevada, which wall the Great Basin on the east and the west. Within the 

 Great Basin there are many mountain ranges, some of them of great size. 

 The greater of these are the Humboldt and the 'Inyo. ranges. On these 

 basin ranges many streams rise and flow down upon the floor of the basin. 

 The precipitation in the Great Basin region is mainly in the winter and 

 spring. At times of abundant precipitation and rapid melting of the snow 

 many ephemeral streams form upon the floor of the basin itself. The 

 streams, small and great, all fail to reach the ocean; the larger of them 

 flow into the permanent lakes of the basin, such as Great Salt Lake, Mono 

 Lake, and Winnemucca Lake, but by far the greater number flow into the 

 ephemeral lakes. These lakes, which are numbered by hundreds, are 

 shallow; they may be many miles across in early spring and entirely 

 disappear before autumn. Also, the permanent lakes, like Great Salt Lake 

 and Winnemucca Lake, greatly expand at the time thev receive the large 

 contributions from the streams and shrink during the summer and autumn. 

 All the streams bring their contributions of soluble materials to the lakes 

 and, in addition, the usual amounts of mechanical sediments. Hence there 

 is mingled in the Great Basin lakes the greatest variety of materials. 

 The salts of alkalies, the salts of the alkaline earths, and lesser amounts of 

 other soluble salts are all commingled with one another and with the 

 mechanical sediments. 



When the waters of the ephemeral lakes are evaporated, all the 

 materials held in solution and in suspension are thrown down. In the 

 larger of the ephemeral lakes there is a distinct tendency for the chemical 

 and mechanical sediments to be deposited in alternate layers. Within a short 

 time after the flood season of spring the mechanical sediments are largely 

 laid down. During the dry season the lake evaporates and the chemical 

 sediments are precipitated. These sediments, while perhaps parti}' dissolved 

 by the waters of the lake of the succeeding flood season, are largely buried 

 under the mechanical sediments of that year. Upon these mechanical 

 sediments follows the next layer of chemical sediments, and so on. 



It is difficult for one who has not traveled in the Great Basin region to 

 appreciate the vast amount of alkaline material deposited by the ephemeral 



