112 LAKES OF NORTH AMERICA. 



and beauty of their structure. Nowhere else in this country, and so far 

 as reported, nowhere else in the Avorld, are rocks formed of precipitates 

 from lake waters so magnificently displayed as in the desert valleys of 

 Nevada. 



The fascination of the weird and frequently wonderfully impressive 

 scenery of the region formerly submerged beneath the waters of Lake 

 Lahontan, is enhanced, at least to the geologist, by the fact that there is 

 3^et an unsolved mystery connected Avith the tufa deposits that start out 

 as strange, gigantic forms from the desert haze, as one slowly traverses 

 those bitter, alkaline lands. 



It is believed that we understand how the more compact and stone- 

 like variety of tufa was deposited, since similar accumulations are formed 

 where waters saturated with calcium carbonate deposit that salt on account 

 of the loss of carbonic acid. The Dendritic tufa may also have been pre- 

 cipitated in a similar manner, or perhaps through the agency of low forms 

 of plant life. The mode of origin of the tufa with well-defined crystals, 

 however, is still unknown, although both geologists and chemists have 

 sought diligently to discovei* the secret of its formation. The open cellu- 

 lar structure of the crystals, as well as their forms, suggest that they are 

 pseudomorphs, that is, having a false form, or a form not assumed by cal- 

 cium carbonate on crystallizing, but resulting from the alteration or 

 replacement of some other mineral. This suggestion only removes the 

 difficulty one step farther, however, since the nature of the original min- 

 eral is still unknown. A more definite statement of this problem ma}^ be 

 found in a special report on Thinolite, by E. S. Dana, who has put the 

 matter in a clearer light than had previously been done.^ 



One of the most remarkable facts in connection with the history of the 

 Lahontan basin, is that the present lakes within it, which might be sup- 

 posed to be remnants of the ancient water-body left by incomplete evap- 

 oration, and therefore intensely saline, are in reality scarcely more than 

 brackish. As shown in the table of analyses of saline lakes given on 

 page 72, Pyramid, Winnemucca, and Walker lakes, the representative 

 water bodies now existing in the Lahontan basin, carry only a small frac- 

 tion of one per cent of saline matter in solution. We know that Lake 

 Lahontan did not overflow. All of the saline matter carried into it, 

 therefore, must still l^e retained in its basin. The vast quantity of vari- 

 ous salts, and especially of sodium chloride, sodium sulphate, and sodium 



1 " Crystallograpliic Study of the Thiuolite of Lake Lahontan," Bulletin No. 12, U. S. 

 Geol. Survey. 



