280 THE JOURNAL OF GEOLOGY. 



mostly dried up, and the only remains of them now are a series of 

 much smaller lakes, occupying hollows in the bottoms of the old 

 lake basins. Great Salt Lake is the modern representative of Lake 

 Bonneville ; and Tahoe, Winnemucca, Pyramid and other lakes 

 occupy the basin of Lake Lahontan. 



The region about the manganese deposit is on the eastern 

 edge of the area defined by Mr. Russell as the ancient bed of 

 Lake Lahontan, and occupies a position at the head of what was 

 once a small bay protruding about fifteen miles up what is now 

 the valley of the Humboldt River. Mr. Russell,^ in speaking of 

 the lakes which formerly existed in the Great Basin, says : 

 "Some of these old lakes had outlets to the sea, and were the 

 sources of considerable rivers, others discharged into sister 

 lakes ; a considerable number, however, did not rise high enough 

 to find an outlet, but were entirely inclosed, as is the case with 

 the Dead Sea, the Caspian, and many of the lakes of the Far 

 West at the present time." Lake Lahontan did not overflow, 

 and, therefore, the mineral matter brought to it in solution by 

 tributary waters constantly increased in quantity; while the grad- 

 ual evaporation of the lake steadily concentrated these mineral 

 solutions until they arrived at a state of supersaturation, and were 

 deposited as chemical precipitates. These were, according to 

 Mr. Russell, largely of a calcareous nature, and were laid down as 

 fringes on the margin of the lake at successive stages of evapora- 

 tion. They are found now at different levels on the old lake 

 border, and mark the ancient shore lines. Mr. Russell has divided 

 them into three classes of "tufas," differing considerably in 

 physical character, and deposited at different levels during the 

 desiccation of the lake. He has named them in the order of 

 their chronological succession, "lithoid," " thinolitic," and "den- 

 dritic" tufas. From the analogy of the samples of tufa col- 

 lected by the writer at the manganese deposit with the description 

 of lithoid tufa given by Mr. Russell, and from the position that 

 the deposit occupies in the old Lake Basin, it is probable that 



' Geological History of Lake Lahontan, A Quaternary Lake of Northwestern 

 Nevada, Monograph U. S. Geological Survey, No. XI., 1885, page 6. 



