432 DESCRIPTIVE GEOLOGY. 



with regard to it. Of the great climatic oscillations, traces are seen in the 

 lake-terraces, which stretch along the flanks of the surrounding mountains, 

 and show that at one period the waters of the lake were over 900 feet 

 higher than at present. With regard to the changes in the height of the 

 water-line from year to year, which are dependent on the varying relation 

 of atmospheric evaporation to condensation, it is impossible to obtain abso- 

 lutely accurate data, since up to the year 1869 no fixed datum-point had 

 been established by which this height could be determined. It is known, 

 however, from information obtained from the Mormon settlers and others, 

 with regard to the water-line on different shoal portions of the lake, that 

 during the eight years preceding the date of our survey of the lake (1869), 

 there had been a general rise of about 11 feet in the level of the waters of 

 the lake. The remarkable flatness of its immediate borders is well shown 

 in the great increase of surface covered by the waters produced by this 

 comparatively slight change of level. The superficial area of the lake, 

 excluding the islands, as shown by this map, is 2,360 square miles, an 

 increase of about 40 per cent., or 660 square miles, over that given by 

 Stansbury's map,^ which is only 1,700 square miles. It is true that Stans- 

 bury's survey was made in 1849-50, or 11 years earlier than the time from 

 which the rise of 11 feet is dated; but it is evident, from the depth of water 

 found at given points along his shore-line, that the level of the surface in 

 1861 must have varied but little, if any, from that of 1849. 



One of the most striking peculiarities of this lake is the great density 

 and pungent bitterness of its waters. This is practically shown by the fact 

 that the human body floats up entirely on the surface like a cork, and that 

 the pain produced by water which enters the eye is almost blinding. It is 

 generally stated by the Mormon settlers that during the early days of their 

 settlement they used to obtain one barrel of salt from three barrels of water. 

 The water obtained by Stansbury in 1850 contained 22.4 per cent, of min- 

 eral salts. In 1869, the solution had become much diluted by the addition 

 of so great an amount of fresh water, and it contained, as will be seen, only 

 14.8 per cent, of solid matter. 



An analysis of several gallons of the water of Salt Lake, obtained by 

 our parties in the summer of 1869 from near Black Rock Point, where the 

 1 Stansbury's Expedition to the Great Salt Lake, 1852. 



