co:ntemporaneity of thyskjal events 371 



menibered that a lowering of oiil}^ three degrees in the present mean 

 annual temperature would induce glacial conditions in the Scottish High- 

 lands, and that a similai" reduction of 12 degrees in the upper Mississippi 

 Valley would cover that region witli the same great continental ice-sheet 

 that characterized it in Ivansan times', it is readily inferred that the 

 production of the relatively insignificant glaciers on the AVasatch and 

 Uinta Monntains would not require necessarily a very marked change of 

 temperature nor a notable increase in regional humidity over that now 

 existing. 



Expressions of Arid erosive Influences 



mastery of desert erosional agencies 



Tn late years our notions concerning land sculpture in arid tracts have 

 undergone great change. Throughout sucli regions the conditions which 

 obtain under normal moist climate no longer prevail. Wholly different 

 processes attain ascendency. Phenomena of the desert which once were 

 seemi]igly hopelessly inexplicable now genetically resolve themselves into 

 their developmental stages, llecognition of tlie tremendous potency of 

 tlie winds as an erosional po^ver under conditions of excessively dry cli- 

 mate puts a new aspect on the derivation of all laii(lsca[)e features of the 

 arid lands, liecent discussions on these phases of the sul)ject need not, 

 however, be reiterated liere. 



DESTRUCTION OF ANCIENT LAKE TERRACES 



The occurrence of tlie okl lake terraces on the flanks of the Wasatch 

 Mountains which constituted the eastern shore of the lake, and on pro- 

 tected sides of other mountains, gives rise to much speculation as to the 

 cause of this peculiarity in their distribution. At first Gilbert thought 

 that he had found an ade(|uate ex])lanati()n by attributing the phenomenon 

 to pixn'ailing westerly wiinls. Later the same author was inclined to the 

 view that there was close sym])athy l)etween the magnitude of the shore 

 features and the fetch of the efficient \va\es, ajid that the greater the dis- 

 tajice through which waves travel to reach a given coast the greater the 

 work accomplished b}' them. This generally recognized principle only 

 partly explains the local situation. The strictly desert influences are not 

 takeJi into account; and, after all, tlie question is ]iot really answered. 

 The question of the preservation of the terraces in some places to the 

 present time remains untouched as ever. 



Hy nil principles of known desert corrasion the terraces of Lake Bonne- 

 ville should lia\e been long since completely obliterated by the action of 



XXVir JWi.i,. (iv.oi.. Soc. A.\f., Vol. 28, U)lc, 



