186 DISCUSSION OF THE DESICCATION QUESTION. 



gested, except under a very different climate, or by evaporation from a 

 melting glacier." * In this statement it is in reality assumed that a larger 

 supply of water than that now flowing in our rivers could not be occasioned 

 in any other way than by the melting of ice. Tiiis is equivalent to taking 

 the position that there can be no changes of climate except such as are regis- 

 tered in the accumulation and subsequent thawing of ice-masses. 



Professor N. H. Winchell, in speaking of the effects resulting from the dis- 

 solution of the great glacier, which he had previously described as having 

 been spread over the whole northern portion of North America, indicates the 

 phenomena which would follow the melting of the ice in these words : '' The 

 turbid streams would be vastly larger than those Avhich occupy the same 

 beds to-day. They would run with tenfold more violence." f 



According to the same author, terraces are due solely to floods along the 

 rivers and lakes, consequent on the melting of the " great glacier." 



Mr. S. F. Emmons, in indicating the magnitude of the erosion which has 

 taken place in the Green River basin since Pliocene times, says : " The bulk 

 of this material must have been carried away by the floods which followed 

 the Glacial period, while at the present day, under conditions of compara- 

 tively slight precipitation, the amount removed from the basin region by the 

 actual agency of water is relatively slight." t 



Mr. G. K. Gilbert, in his description of the former condition of things in 

 Great Salt Lake Valley, § alluding to the once greatly enlarged area of that 

 lake, says: "There can be no doubt, then, that the great climatal revolution, 

 which covered our nortlieastern States with ice, Avas competent to flood the 

 dry basin of Utah ; and that it actually did so is highly probable." || 



From the last paragraph we see tliat it was the opinion of (he author 

 quoted that the Salt Lake i-egion had been an arid one previous to the 

 Glacial epoch, and tliat synchronously with this, and under the action of the 

 same causes, the lake became greatly extended in area. According to Mr. 

 Emmons's views, as will be perceived, it is the entire Glacial epoch which 

 is the period of greater precipitation, and its cessation, simply, which is the 

 cause of desiccation. 



* Thi; Trenton Gra\'fl, and its Helation to the Anticjuity of Man. By Henry Carvill Lewis. From the Pro- 

 ceedings of the Aeadeniy of Natural Sciences of rhiladelpLia. A piper read Nov. 24, 1879. 

 + The Drift-Deposits of tlie Northwest. Popular Science Monthly for June and July, 1873. 

 J Fortieth Parallel Survey Report, Vol. II. p. 206. 

 § See ante, p. 106. 

 II United States Engineer Reports of Explorations, etc., west of the 100th Meridian, Vol. III. p. 96. 



