GEOLOGICAL CRITICISM 
315 
Despite full recognition of the originality of the modern idea of eola¬ 
tion brought out by Hill, Udden, Cross, and Free, but ofi which Keyes is 
the principal exponent, and while seeing in this idea a way to the explan¬ 
ation of phenomena otherwise obscure, I am more impressed by this 
paper than any other of Keyes’ productions that in the enthusiasm of the 
new idea he underestimates the importance, and virtually denies the signi¬ 
ficance, of certain plain facts — chiefly the unmistakable evidence of water 
sculpture throughout the greater part of the region to which his discus¬ 
sion applies. To make my meaning clear, I note a few examples. 
For two-thirds or three-quarters of the length of the Southern Pacific 
Railway between Deming and Yuma that railway traverses plains which 
in the rough way seem approximately horizontal, but which are always 
inclined and represent slopes conformable with (and evidently due to) 
the running water of the region. The fact that they conform with the 
running water is established by observation of residents and of critical 
travelers; but it is demonstrated beyond all peradventure by devices em¬ 
ployed to protect the railway against sheetfloods, in which most of the 
running water of the region moves — for while the nature of the floods 
seems not to have been recognized by the engineers, it has been by the re¬ 
spective section-bosses who have worked out their own devices for pro¬ 
tection— the most effective being extended wing-dams reaching from 
occasional culverts obliquely up-slope to finally meet with the corre¬ 
sponding wing-dam running up from the next culvert. In a broad way, 
more work has been required to construct these protective devices than 
to build the railway grade; and they attest the practical recognition on 
the part of railway attaches of the great fact that the broad plains 
traversed by the railway are not only water-shaped but are subject to 
overflow (tending to continue the shaping process) every year. 
The approximately east-west divide between the streams flowing toward 
the Gila and those running directly toward the Mexican Gulf, nearly 
coincides with the international divide from Nogales westward; and 
there is a pronounced difference in topography on opposite sides of this 
divide, evidently due first to continental uplift producing a south-western 
tilting, and second to water sculpture as influenced by this tilting. North 
of the divide the intermont plains are comparatively smooth, whether of 
planed rocks (due to sheetflooding, in my judgment) or of alluvial ac¬ 
cumulations in the central valleys. South of the divide the intermont 
plains are more deeply sculptured, and over something like three-quarters 
of the entire surface are molded into southwesterly sloping terraces or 
mesas, forming the most conspicuous' feature of the average landscape. 
Many of the streams (albeit more or less ephemeral) have under the 
stimulation of the southwesterly tilting retrogressed entirely through 
transverse sierras; and after such retrogression they have continued 
working headward into the invaded intermont plain, developing a config¬ 
uration conspicuously of the dendritic, wide-branching type due to water 
sculpture. The prettiest example known to me of this invasion of smooth 
