298 King’s Systematic Geology of the 40th Parallel. 
From the fact that the sediments of these lakes are under- 
laid and overlaid by subaerial gravels, both King and Gilbert 
infer that there was a very wet period between two dry peri- 
ods. But our author goes much further, and from the results 
of a study of the chemistry of the waters, as expressed in the 
soluble contents of the remaining lakes, and in the natural 
evaporation products, constructs an ingenious and it would 
eem a well-founded hypothetical climatic bistory of the Qua- 
ternary period. The argument may be briefly outlined. The 
now dry shores of the ancient Lake Lahontan are in many 
places covered, sometimes twenty to sixty feet deep, with a 
tufaceous deposit,.which is often distinctly crystaliized and then 
shows the very characteristic forms of gaylussite—a hydrated 
earbonate of soda and lime. But chemical analyses show 
that the soda and water are gone, and that the mineral is now 
calcite—only the external form being that of gaylussite. In 
short, we have here an instance of pseudomorphism on a large 
scale. This pseudomorphous material King calls Thinolvte. 
Near Ragtown, Nevada, in a lake which is one of the remnants 
of Lahontan, and which is presumably fed by springs, the 
forming of gaylussite can now be seen in operation. It is a 
dense water very rich in soda carbonate, and when the lake 
shrinks during the dry season, gaylussite crystals are deposited 
on the beach and on floating organic substances. Both the 
facts at this lake and Fritsche’s experiments show that gaylus- 
site can form only in the presence of a large excess of carbon- 
ate of soda. When the saline water of this lake is diluted dur- 
ing the wet season, the gaylussite is dissolved again. 
The thinolite tufa occurs up to an altitude of 470 feet above 
Pyramid Lake, or within thirty feet of the highest known level 
of the extinct Lahontan Lake. The inference from this is that 
the lake must have been long exposed, without an outlet, to 
concentration by evaporation, and perhaps by contributions 
from alkaline springs, in order to deposit gaylussite at such an 
altitude ; and, in order to have formed the vast deposits of tufa 
—originally gaylussite—the lake must have almost wholly 
evaporated. Now the evaporation of a sea, which, with a depth — 
of 470 feet, was sufficiently saline to deposit gaylussite, would 
leave its residuary lakes in the condition of saturated solutions ; 
but the fact is that the larger relics of Lahontan, viz: Pyramid 
and Winnemucca Lakes are sufficiently fresh to support 
numerous fishes, including one or two of the Salmonide. It 1s 
evident, therefore, that the residuary water of the evaporation 
of Lahontan, that produced these tufas, must have wholly dis- 
appeared. This could only take place by the basin filling to 
its outlet and remaining at that altitude long enough for its 
dissolved salts to drain off and for the water to become 
