316 
GEOLOGICAL CRITICISM 
plain by retrogression of a river through a range is a few miles south of 
the international boundary, near the mining camp located by Professor 
Blake some yeas ago; it is some twenty or thirty miles west of the Mexi¬ 
can custom house at Sasabe. It was mapped in some detail for me by 
Willard Johnson, but unhappily his failure of health prevented comple¬ 
tion and publication of the map. A somewhat more accessible example 
appears at Sasabe; there the retrogression has been through a general 
mountain mass rather than a distinct sierra, but the change in configura¬ 
tion from the Mexican custom house to the American' custom house at 
Buena Vista (which is just on the interment divide) is striking, while the 
great water-cut slopes extending southwestward are conspicuous in the 
country extending from Sasabe to Altar. The most conspicuous example 
of river retrogression through a range is a hundred miles further south¬ 
ward, where Rio Boccuache has cut a narrow gorge through a lofty sierra; 
its head drainage has deeply sculptured the intermont plain generally pro¬ 
tected by that range; in the gorge the ground water is brought to the 
surface by the little pervious rocks, so that this part of the stream is 
perennial while both above and below it is commonly a mere sandwash. 
These examples might be multiplied; but it suffices to say that they are 
typical and express the general fact that fully two-thirds or three-quarters 
of the surface throughout the hundreds of thousands of square miles of 
desert known to me are manifestly shaped primarily by water sculpture — 
albeit generally by sheetfloods rather than by streams. 
Throughout the region contemplated by Keyes, and as I have seen it, 
the conspicuous feature of the sierras is ruggedness; they not only rise 
sharply from the plains as he describes but rise deeply in cliffs, picachos, 
and minor and major crests, generally o^ bare rock, sometimes displaying 
the characteristic exfoliation forms of granite, but more commonly sculp¬ 
tured into the distinctive forms produced by water-action — indeed no¬ 
where else do I know of mountains so eloquently attesting energetic 
storm-water work as those of the arid region. This is not an exceptional 
case, but the common one — indeed it is characteristic of the entire region 
as known to me. 
;Now in the light of these facts I can not help feeling that Keyes la3"s 
himself open to criticism and opens his conclusions to distrust, by vir¬ 
tually denying that the configuration of the arid region is explicable, save 
on the supposition of a predominant deflation. I think I see how his 
mind is influenced — perhaps obessed — by the idea of deflation to such 
an extent that his mental pictures emphasize those facts and features of 
configuration which deflation explains; but with a view to his own pro¬ 
tection against criticism no less than with/ a view to the correct inter¬ 
pretation of nature, it is desirable that he should guard his expressions 
more carefully and especially avoid denial of the existence of evident facts 
attesting water sculpture — facts which in their geographic extent are far 
greater than those attesting deflation. 
Of course I recognize that Keyes through deflation supplies the missing 
