830 



SCIENCE 



[N. S. Vol. XL. No. 1040 



Assuming that the calcium has been brought 

 into the Lahontan Basin in the same ratio to 

 the sum of the sodium, and potassium as it is 

 being brought in by the present rivers and 

 calculating how much calcium carbonate 

 would have to be deposited to have main- 

 tained the same ratio to the sodium and po- 

 tassium in the present lakes gives in round 

 numbers one hundred million tons. As this 

 figure is approximately the same as the 

 amount of tufa deposited, it indicates that 

 Pyramid Lake is a remnant of Lake Lahon- 

 tan and that the latter has never been com- 

 pletely desiccated. 



If this be true it is possible to approximate 

 the age of Lake Lahontan by computing the 

 number of years necessary for the Truckee 

 River, the only important stream at present 

 flowing into Pyramid and Winnemucca lakes, 

 toi carry into the lakes the amount of salt at 

 present in solution. Several independent de- 

 terminations were made, using the total solids, 

 and such of the individual salts as were 

 likely to have suffered little loss through 

 deposition. Of these the chlorine gave the 

 maximum figure, 4,500 years, while the others 

 ranged from a thousand to 2,500 years. Un- 

 fortunately the Truckee flows also into Win- 

 nemucca Lake and there is some evidence that 

 the latter may have been desiccated since the 

 beginning of Lake Lahontan. Further, in 

 times of high water Pyramid Lake has dis- 

 charged into Winnemucca and it is uncertain 

 how much saline material may have been lost 

 by burial in the Winnemucca basin, if any. 

 Judging from the correspondence between 

 the actual amount of tufa deposited and the 

 amount that should have been deposited, as 

 indicated by the amount of salines stiU pres- 

 ent in the lake waters, it is believed that the 

 loss from this source has been slight. 



A comparison of the total solids in the lakes 

 to-day with those present at the time of Rus- 

 sell's visit when the lake was practically at 

 the same level gives two thousand years as 

 having elapsed since the basins first began to 

 fill. From these concordant results it is prob- 

 able that Lahontan first began to form within 

 the last five thousand years. 



There is abundant evidence of the compar- 

 ative recent formation of the terraces, beach 

 lines, and other shore phenomena of the an- 

 cient lake in their freshness and absence of 

 erosion. Even where there is a considerable 

 drainage basin behind them the terraces are 

 barely notched by the streams that cross them 

 and any one who is familiar with the erosive 

 power of the not infrequent cloudbursts of 

 Nevada can but wonder that the records of the 

 old lake have stood so long without extensive 

 defacement. Although faulting is still in 

 progress, yet the shore lines and sediments of 

 Lahontan have suffered little displacement. 

 Careful measurements of the elevation of the 

 terraces in different parts of the basin show 

 them to still be horizontal. 



Estimates go to show that if the rainfall of 

 the drainage basin increased to somewhat less 

 than double the present rainfall the Lahontan 

 Basin would again fill to its former level. 

 The recent work of Huntington'' with the big 

 trees of California indicates that there was 

 such an increased rainfall in the immediate 

 vicinity of the Lahontan Basin at the time it 

 is believed the old lake was at its height. 



While the work is still in progress yet it is 

 so nearly finished that it is not believed that 

 the above conclusions will be materially modi- 

 fied. The conclusion that Lahontan has never 

 been completely desiccated and that the waters 

 of Pyramid and Winnemucca lakes are resid- 

 uals makes it possible to forecast the amounts 

 of potassium deposits in the portions of the 

 Basin that are at present desiccated. An esti- 

 mate made for the Black Rock Desert indi- 

 cated that if all the potash deposited from 

 Lahontan were segregated in a single square 

 mile it would form a deposit only three inches 

 thick, and if potash beds are found in this 

 desert they must have been formed in the 

 buried sediments of a lake of which we have 

 no knowledge at present. 



J. Claude Jones 



Univeesitt of Nevada, 

 Eeno, Nev. 



5 Huntington, Ellsworth, Eept. of Smithsonian 

 Inst., for 1912, pp. 383-412, 1913. 



