RELATION OF LAKES TO CLLMATIC CONDITIONS. * 87 



witli a twilight glow. In these elevated regions Muy-day is a festival of 

 late summer, but it brings with it a multitude of charms that are unknow.i 

 to dwellers in the world below. 



The mountains hold out innumerable charms to detain us, but we 

 must descend in our fireside journey, and leaiui more of the strange lake, 

 the setting of which was revealed from our station on the mountain top. 

 Our downward journey is through a deep goige with nearly vertical walls; 

 in its bottom a swift, clear stream plunges from ledge to ledge, and rushes 

 through rocky chasms with a roar that never allows the echoes of the 

 cliffs a moment's pause. This pure stream of cold, delicious water reveals 

 the character of many creeks and rivulets that are rushing down the 

 mountain side to the ever-thirsty valley below. 



A few springs add -their waters to tlie supply from the mountains, 

 but none of them are saline, and their united volume is far less than the 

 volume of any one of half-a-dozen of the mountain torrents pouring into 

 j\Iono lake. The present density of the lake water is the result of the 

 long concentration by evaporation of the supply from the mountains. 



The area of ]\Iono lake in the summer of 1883, was 87 square miles, 

 1)ut varies with the seasons and also from year to 3'ear. As may be 

 learned from the accompanying map, its north and south axis measures 

 11, and its east and west axis 14 miles. Its surface is broken by two 

 volcanic islands and by numerous crags, some of which are remnants of 

 islands now nearly eroded away, while others are formed of calcareous 

 deposits precipitated about sulnnerged springs. The soundings given 

 on the map, show that its maximum depth is 152 feet, and the mean 

 depth about 61 or (32 feet. Its elevation above the sea, when surveyed 

 in 1885, was 6380 feet. 



In Pleistocene times, when great glaciers descended from the High 

 Sierras and were prolonged several miles into the valley, the ratio between 

 iiillow and evaporation was changed, and the lake rose, but never suffi- 

 cieiitlv to discover an outlet. During the time of its greatest e\])ansion, 

 it had ail area of 316 s(piare miles, and formed an unbroken water surface 

 28 miles h)ng from north to south, and 18 miles l)i-oad. Its maxinnim 

 dejjtli was then over 800 feet. 



Tlie facts of greatest interest in connection with ^Nlono lake are to be 

 found in its cliemical liistory. As shown in tlie analysis of its waters 

 given on page 72, it is strongly impregnated with sodium and with tar- 

 bonie and sulphuric acids. The most jnohable coinliination of these and 

 other substances present in the waters is given below : 



