392 PROCEEDINGS OF THE CALIFORNIA MEETING 



ORIGIN OF THE TUFAS OF LAKE LAHONTAN 

 BY J. C. JONES* 



(Aistract) 



In the earlier study of the history of Lalie Lahontan, Professor Russell be- 

 lieved that the tufas were chemical deposits caused by the saturation of the 

 lake waters with calcium carbonate. A study of the recent tufa forming in 

 the Salton Sea led to the conclusion that the deposit was due to the activities 

 of blue-green algie. Carrying the research into the Lahontan Basin, it was 

 found that the algfe were responsible for the tufa forming at present about 

 the shores of Pyramid Lake. An examination of the dendritic and lithoid 

 tufas of Lahontan age disclosed the remnants of algje in the tufa. Other lines 

 of evidence indicated that the tufa was formed by the algie, the only essential 

 difference between the lithoid and dendritic types being that the latter was 

 apparently formed whenever and wherever the conditions of growth were 

 more favorable for the algse. 



Measurements of the more perfect thiuolite crystals showed that they origi- 

 nally formed as aragonite crystals, and it was discovered that when the water 

 from Pyramid Lake was saturated with calcium carbonate similar crystals of 

 aragonite were deposited. It is concluded that the waters of Lake Lahontan 

 approached saturation with respect to calcium carbonate only at the time that 

 the thinolite was deposited, and that the history of the ancient lake as written, 

 based on the origin of its calcareous deposits, will have to be modified. 



Discussion of this paper was deferred. 



The session adjourned at 12.10 p. m. to convene after the session of 

 the Paleontological Society. 



The Society convened at Bacon Hall, University of California, after 

 the meeting of the Paleontological Society, 28 members and visitors being 

 present. 



SOME PHYSIOGRAPHIC FEATURES OF BOLSONS 

 BY HERBERT E. GREGORY 



Read in full from manuscript by Prof. C. F. Tolman, Jr. 



Discussion 



Prof. C. F. ToLMAX, Jr., discussed five types of wind erosion, as follows: 

 Protected surfaces — (1) by vegetation; (2) coarse gravel and boulders; cites 

 boulders 1 foot in diameter S miles from mountains, near Tucson, Arizona ; 

 (3) caliche and surface cements 1 to 6 feet thick; (4) desert pavements — 

 sheet of pebbles left on wind-swept surface as mosaic; (5) clay in bottom of 

 playa becomes polished and hardened, protecting from erosion of wind. 



Introduced by J. C. Merrlam. 



