108 THE DESICCATION OF LATEE GEOLOGICAL TIMES. 



In point of fact, Mr. Gilbert, in the communication from which the above 

 extracts have been made, acids but little to what wa.^s previously known in 

 regard to the phenomena of desiccation in the Great Basin region. He con- 

 firms the previously observed fact of the former much greater size of Great 

 Salt Lake, and adopts the view maintained by the present writer, several 

 years before, in regard to the climatic character of the change, and its con- 

 nection with the Glacial epoch. 



The Fortieth Parallel Survey, under the direction of Clarence King, 

 added much more to our knowledge of the facts connected with the 

 desiccation of Great Salt Lake, as Avell as of other portions of the re- 

 gions Avest of the Rocky Mountains.* Some of the theoretical views 

 advocated by the chief of that Survey, in his volume resuming the geo- 

 logical results of that great Avork, Avill be noticed further on : at present 

 we have only to do with those facts stated by him Avhich bear on the subject 

 before us. But, in the first place, it will be proper to quote what is stated, 

 as the net result of the investigations which this Survey, in regard to the 

 former glaciation of the regions, embraced within their field of inquiry. The 

 conclusions arrived at, and which are Avholly confirmatory of those of the Cali- 

 fornia Survey, are as follows : " Wherever in the Fortieth Parallel area a 

 considerable mountain mass reached a high altitude, especially Avhen placed 

 where the Pacific moisture-laden wind could bathe its heights, there are 

 ample evidences of former glacial action, but the type is that of the true 



mountain glacier, AA'hich can always be traced to its local source On 



the drier interior parts of the Cordilleras the ancient glaciers usually ex- 

 tended down to between 7,000 and 8,000 feet above the level of the sea. In 

 the case of the Cottonwood glacier of the Wahsatch, a decided exception, the 

 ice came down to an altitude of 5,000 feet."t 



Bat Avhat Ave have to do Avith at present is, the evidence of recent diminu- 

 tion in the dimensions of the lakes of that part of the Great Basin and of the 

 Rocky Mountains embraced within the "Fortieth Parallel area "$ and ad- 

 jacent to it. In regard to this point the information given in Mr. King's 



* See Fortieth Parallel Survey Report, Vol. I., Sj'stematic Geology, Section V., Quaternary, p. 459, et seq. 



+ In the volume quoted above a diagi-am is given showing that portion of the surface adjacent to the fortietji 

 parallel which was formerly covered with ice. It forms but a very small fraction of tlie whole area embraced within 

 tlie field of the Survey. 



t The "Fortieth Parallel area," or the belt of country embraced within the field of Mr. King's Survey, is 

 essentially all tliat portion of the Cordilleras which lies between the fortieth and forty-second parallels, and east 

 of the crest of the Sierra Nevada. 



