STUDIES OF SPECIAL LACUSTKAL HISTORY. Ill 



surface of the present lake. The rehition of the tufa deposits and the 

 terraces with which they are associated, are shown in the following diagram. 



Lahontau Beach 530 feet. 



Lithoid Terrace 500 " 



Dendritic Terrace 320 " 



Thinolitic Terrace 110 " 



Surface of Pyramid Lake, 1882 . . " 



Fig. 9. — Diagram SHO\\rrNr, the relation of the Terraces of Lake Lahoxtan 

 TO Pyramid Lake. 



The Lithoid tufa near its upper limit is seldom over eight or' ten 

 inches thick, hut increases to ten or twelve feet on the lower slopes* The 

 Thinolite is usually from six to twelve feet thick. The Dendritic variety 

 is tlie heaviest of all and frequently appears on steep slopes in imbricated 

 layers from fifty to sixty feet thick. In some favorable locality the entire 

 tufa deposits have a thickness of at least eighty feet, and in rare places 

 near the surface of Pyramid lake and partially concealed by its waters, 

 there is evidence that these deposits are still more massive. The total 

 amount of calcium carbonate deposited from the ancient lake can only be 

 estimated in millions, if not billions of tons. 



Every island and rocky crag that xose in Lake Lahontan became a cen- 

 ter of accumulation for tufa deposits and was transformed into strange and 

 frequently fantastic shapes by the material precipitated upon it. Now 

 that the waters of the ancient sea have disappeared, these structures stand 

 in the desert valleys like the cruml)ling ruins of towers, castles, domes, and 

 various other shapes, in keeping with the desolation surrounding them. 

 The finest examples of these water-built structures, some of them a hun- 

 dred feet or more in height, occur about the border of Pyramid and 

 AVinnemucca lakes (Plate 20), or rising from their bottoms and still 

 wholly or in part submerged. The islands in Pyramid lake are sheathed 

 from base to summit with these deposits and their precipitous sides given 

 a convex outline, owing especially to the vast deposits of Dendritic tufa, 

 which was precipitated most abundantly midway up the slopes. Tlie 

 most remarkal)le of these islands, and the one from wliicli tlie lake derives 

 its name, is shown in the sketch forming Plate 23. When tlie tufa towei"S 

 and castle-like piles are broken, the concentric layers of which they are 

 composed are revealed and fill one with wonder nt the vast aiiionnt of 

 matei'iiil ihev contain, as well as attract the eye on at-count of lite delicacy 



