340 



PRINCIPLES OF STRATIGRAPHY 



best developed. Similar crystals are found in the deposit of the ex- 

 tinct lake of .Mono Valley, California. The last deposit is the 

 Dendritic tufa, and it is also the most abundant. Its greatest depth 

 is more than twenty feet, and may be as much as fifty. (Fig. 65.) 

 Between Wadsworth and Pyramid lakes, the old floor of Lake La- 

 hontan is completely covered over an area of several square miles 

 by dome-shaped masses of this tufa, commonly spreading in mush- 



FiG. 65. 



Tufa domes, shore of Pyramid Lake, Nevada. 

 Lahontan. The deposit is of dendritic tufa. 



A remnant of Lake 

 (After Russell.) 



room fashion, and up to 5 or 6 feet in diameter. (Fig. 66.) In- 

 terference with one another's growth produces polygonal outlines. 

 This is the case on Carson River, where they sometimes form a 

 pavement of hexagonal blocks, each about 2 feet in diameter. The 

 dendritic character of this tufa is seen on weathered surfaces. 

 Where embedded in the gravel or silt deposits of the lake or the 

 interpolated river sediments, these tufa deposits form definite lime- 

 stone horizons, with or without fossils, these limestones horizons be- 

 ing indicative of desert conditions, under which they were chemi- 

 cally precipitated. 



