DESICCATIOX AS COXXECTED WITH THE CxLACIAL EPOCH. 107 



surfixce in any one general direction. He remarks on this point as follows : 

 " The unrnflled repose of all snch unconsolidated beds in Nevada and ad- 

 jacent Utah is proof positive that no general glaciation has prevailed 



We may conclude, without reservation, that the great ice-field of Eastern 

 North America had no counterpart in the same latitude at the West." After 

 describing some of the phenomena of former local glaciation about the crests 

 of the highest ranges in Nevada, his results and inferences agreeing in the 

 main with those of the present writer and of the geologists of the Fortieth 

 Parallel Survey, Mr. Gilbert goes on to speak of the diminution in area of 

 Great Salt Lake and of other bodies of water in the Great Basin. These 

 changes he describes in a chapter entitled The Glacial Epoch, remarking 

 that " for reasons which will appear in the sequel " he has " come to regard 

 as phenomena of the Glacial epoch a series of lakes, of which the beaches 

 and sediments are to be found at many points in the Great Basin." He then 

 proceeds to indicate, in considerable detail, the former outline of Great Salt 

 Lake at the period of its greatest extension, and to the ancient lake thus 

 bounded he gave the name of Bonneville, in honor of the earliest explorer who 

 brought back any authentic account of the Great Basin region, and of Great 

 Salt Lake in particular. The work of the Fortieth Parallel Survey having 

 superseded that of the Wheeler Survey in this region, it will not be neces- 

 sary to give any detailed account of Mr. Gilbert's observations, but only to 

 state the reasons Avhy this geologist described the phenomena in question as 

 belonging to the Glacial epoch. On this point he remarks as follows : " The 

 Bonneville epoch [meaning the time Avhen Salt Lake was much larger than 

 it now is] and the Glacial epoch were alike climatal episodes, and they 

 occurred in the same general division of geological time, namely, the division 

 of which modern time is the immediate sequel.* .... To account for the 

 origin of Bonneville Lake, we need to assume a climatal change that would 

 increase precipitation or diminish evaporation ; and both of these effects 

 would follow, in accordance with familiar meteorological laws, if the hu- 

 midity of the air were increased, or if the temperature were lowered. There 

 can be no doubt, then, that the great climatal revolution, which covered 

 our Northeastern States with ice, was competent to flood the dry basin of 

 Utah ; and that it actually did so is at least highly probable." 



* jrr. Gilbert omits to mention the fact that this connection of the increased area of the Great Basin lakes 

 wicli the phenomena of past glaciation had been pointed out ten years earlier by the present writer, iu the Geology 

 of California, Vol. I. 



