Keyes — Meteorites 'on the Painted Desert. 135 



The so-called lake-beds are mainly composed of coarse 

 silts. Their great thickness and uniform lithologic char- 

 acter might be difficult to explain were it not for the fact 

 that other depressions exist in the vicinity that still re- 

 tain their waters. A single local "cloud-burst" may fill 

 with water such an enclosed basin to a depth of a dozen 

 or a score of feet, as shown in the sudden rise in the level ' 

 of the Laguna del Perro in eastern New Mexico, 11 the 

 overflow of the Rio Carmen in the San Jose bolson in 

 Chihuahua, Mexico, 12 and the appearance of the ephem- 

 eral lakes in the Rio San Juan valley in Tamalipas state. 

 Zuni Salt-Lake, a few miles east of the Coon Butte, occu- 

 pies a similar crateriform depression in the plain and 

 out of its waters rise two small ash-cones. 



The filling of such ephemeral pools and other bodies 

 of water in the desert must be exceedingly rapid. The 

 well-known playa formations are one phase. Certain of 

 the so-called Tertiary lake deposits of western United 

 States are another. Desert soil accumulations some- 

 times are a third sort. In physical characteristics the 

 resemblance of all of these deposits to the loess is as re- 

 markable as it is genetically suggestive. 



Wind-blown dusts of the desert are caught and retained 

 by bodies of water, and under favorable conditions enor- 

 mous deposits are rapidly built up. The vast boracif- 

 erous clays, 5000 to 8000 feet in thickness, of southern 

 California are thus explained. 13 The great inland sea, 

 or arm of the Pacific ocean, once covering the deep Death 

 valley, the Mojave basin and the Santa Clara valley is 

 regarded as long in drying up. The disappearance of 

 the water may have been more rapid than the great thick- 

 ness of the terranes at first thought suggests, for the 

 reason that as an accompaniment of the evaporation of 

 the waters in an excessively dry climate there must have 

 been a filling-up of the basin by the prodigious quantities 



n Journ. Geol. 16:434. 1908. 



12 Am. Jour. Sci. IV. 16:378. 1903. 



"Trans. Amer. Ins. Mining Eng. 40:674. 1909. 



