222 GEOLOGICAL HISTORY OF LAKE LAQONTAN. 



unfit for drinking. In some instances tufa towers ten or twelve feet in 

 diameter, perhaps occurring in clusters, rise twenty or thirty feet above the 

 bottom where soundings show the water to be forty feet deep. From a boat 

 these structures may be clearly seen when sailing over their submerged 

 summits. At times springs rush upward from openings in the tops with 

 such force that their presence is distinctly marked at the surface by a low 

 dome of water. 



The formation of tufa finds many illustrations in the Mono basin 

 which will be described more completely in a future report. Only a few 

 examples are mentioned here as supplementing those observed in the 

 Lahontan basin. On the southern shore of Mono Lake, near the Mono 

 Craters, there is an area several acres in extent, bordering the lake, that is 

 covered with thousands of slender tubular columns of tufa from a few 

 inches to three or four feet in height. These are porous and tubular in 

 structure, and must have been built up by the deposition of calcium car- 

 bonate from the waters that once rose through them. When the orifice at 

 the top of a column became closed other openings were formed at the side, 

 thus causing the structure to become irregular and sometimes branching. 

 This strange forest of contorted tufa trunks was formed by springs beneath 

 tlie surface of the lake when it stood at a higher level than at present, and 

 has been left exposed by a recession of the waters. 



The similarity in structure between the tufa deposits formed about 

 sublacustral springs in Mono Lake, and the inner core of lithoid tufa in 

 many of the tufa towers now standing in the desiccated basin of Lake 

 Lahontan, is sufficient indication that many of the latter were deposited in 

 a like manner. This explanation, however, cannot be extended to tlie 

 coatings of thinolite and dendritic tufa enveloping the cores of lithoid. 

 From our present knowledge we may conclude that there are at least two 

 ways in which tufa towers may originate. First, by the direct precipita- 

 tion of calcareous tufa about nuclei. Second, from the precipitation of the 

 same material from springs rising in lakes that are highly charged with 

 mineral matter in solution. 



