TUFA DOMKS, CASTLES, AND CRAGS. 207 



indicates that the concentration of the waters of Pyramid Lake at present 

 must approximate that of the ancient lake during its first rise. In sheltei-ed 

 bays among the Needles, where springs with a temperature of about 100° F. 

 rise in sliallow water, there are beaches of creamy- white oolitic sand, which, 

 like the calcareous coating on the rocks, is still in process of formation."^ 

 The calcium composing the oolitic sand is probably derived from the warm 

 springs near at hand, which are also depositing a light-colored, porous tufa 

 on the lake bottom. In a number of instances, tuljular and mushroom- 

 shaped growths occur about the orifices of the submerged springs. Soifie 

 of these irregular tubes rise 5 or G feet above the bottom of the lake, and 

 afford passages for the warm waters that stream through them. It is evi- 

 dent that the precipitation of calcium carbonate commences at this locality 

 at the instant that the warm spring-water comes in contact with the cooler 

 and denser water in which it rises. No chemical examination of these 

 spring waters has been made, but judging from their taste they are prac- 

 tically fresh. The tubular forms produced are high in comparison to their 

 diameter and form miniature towers and domes, which in deep, still water 

 might grow to be of large size. A few of them are represented in Fig. 6, 

 page 61. They assist one in understanding the origin of certain Lahon- 

 tan tufas, which we shall next consider. 



TUFA DEPOSITS IIST THE FOKM OF TOW ERS, D03IES, CA8TEES, CRAOS, 



ETC. 



In the foregoing descriptions our attention has been directed to the 

 layers of tufa sheathing the interior of the Lahontan basin. "We now turn 

 to other deposits of the same nature occurring in isolated positions at vari- 

 ous distances from the borders of the valleys, which we shall call tufa 

 domes, towers, castles, etc., as their forms may suggest. Some of these 

 masses are now wholly or in part submerged beneath the waters of the ex- 

 isting lakes, while others are scattered throughout the desert valleys which 

 were formerly flooded, and frequently resemble isolated watch-towers or 

 crumbling ruins, the origin of which must be a puzzle to one not familiar 



*The general features of this locality have beeu noticed in describing Pyramid Lake, page 60. 



