558 THE FRESH-WATER LOCHS OF SCOTLAND 
eolation, but not very rapid evaporation. Irrigation would produce 
a decreasing fall every year until a balance should be reached between 
the area of the lake and the amount of water it received, when no 
further fall would occur as the result of irrigation. Irrigation was 
in progress during the time that the lake rose rapidly. Talmage 
says that in the dry atmosphere of the Great Basin much of the 
water spread upon the land is lost from the surface by immediate 
evaporation, and little water finds its way to the lake through 
subterranean channels or by springs.^ But a small portion of the 
water lost by evaporation within the area is precipitated again 
therein, the prevailing winds operating to carry it eastward. The 
rise in the lake-level which began after the first settlement of the 
region was in part due to the pasturing of animals in large numbers 
within the drainage basin. The effect was that the soil was trampled 
down, and by thus losing in surface porosity it permitted the water 
to run directly off, and the lake was the recipient of greatly increased 
contributions. The removal of the herbage by cattle, and the defor- 
esting of the hill-slopes by man, further lessened the retention of 
rain-water and snow within the region.^ 
Honey Lake, California ; Pyramid, Winnemucca, Humboldt, 
North Carson, South Carson, and Walker Lakes, Nevada, occur in 
valleys which are deeply filled with the sediment of another ancient 
body of water named Lake Lahontan. 
Honey Lake, the western arm of Lake Lahontan, may be classed 
to-day as a playa lake ; it is without outlet, and becomes completely 
desiccated during seasons of unusual aridity. 
Pyramid Lake, 4890 feet above sea-level, is 30 miles in length 
by 12 miles in maximum breadth ; its area in September 1882 was 
828 square miles. The greatest depth is 361 feet. As the Lahontan 
beach is 525 feet above the 1882 level of Pyramid Lake, the former 
lake had a depth of 886 feet ; this is the deepest point in Lake 
Lahontan. Pyramid Lake is without outlet, and receives almost its 
entire supply from the Truckee River, which enters it at the southern 
end. Near the mouth of the Truckee the waters are sufficiently fresh 
1 Talmage, "The Great Salt Lake," Scott. Geogr. Mag., vol. xvii. p. 630, 190L 
2 See Trimmer, "Rise in the Level of the Great Salt Lake," Geogr. Journ., vol. 
xxxi. p. 568, 1908. The level of the Great Salt Lake at midsummer 1907, after 
the snows had melted on the mountains, was 3 feet 6 inches above zero, the 
highest reading for ten years. A railway was built on piles during the low-water 
period for a distance of 10 miles across the shallows of the northern end of the 
lake, at a height supposed to be beyond the reach of the water, but a further rise 
of 2 feet would submerge the rails. Bearing in mind the steadily increasing 
diversion for irrigation of all streams feeding the Great Salt Lake, the rise now 
under observation seems to be of unusual interest. 
