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eat as oat 
HUNTINGTON AND GOLDTHWAIT: THE HURRICANE FAULT. 215 
tion, assume a curve tangent to it, and finally die out as they become 
horizontal. Everywhere the deposit consists of uniformly fine white 
sand without a trace of pebbles or of coarser sand so far as has yet been 
observed. The uniformity of texture is emphasized by the total lack of 
ripple marks, which, as Cornish (a, p. 280) has shown, result from the mix- 
ture of sand grains of different sizes. That such a formation could be 
due to marine or lacustrine action of any kind seems contrary to what 
we know of such agencies, It is generally recognized that cross-bedding 
of a marked type is a proof that the deposits were formed close to the 
shore or on land. The uniform thickness of the Colob sandstone over 
so great an extent renders it antecedently improbable that it is a shore 
deposit ; the total absence of ripple marks, rill marks, and other charac- 
teristic shore features lends support to this, and lastly the perfect 
smoothness and horizontality of the planes which truncate the tops of 
the strata render this still more improbable. At the time of the forma- 
tion of a given cross-bedded layer which is now fifty feet thick and has 
a dip of twenty-five degrees, the water would have had to be over fifty 
feet deep, since in their untruncated condition the strata must have had 
a greater thickness than at present. The question then becomes: Is it 
possible that in a body of water sixty or more feet deep the waves or 
tides or currents should first carry away five or ten feet of sand, and 
then without disturbing the perfectly smooth surface thus formed lay 
down on it other layers of sand having a dip of twenty degrees and 
rising fifty or sixty feet above the base on which they were deposited ? 
And could this process go on uninterruptedly over an area of thousands 
of square miles? We cannot affirm that it is impossible, but we can 
affirm that it is improbable, and nothing of the kind seems to have 
been observed in actual formation. The same facts of structure, to- 
gether with the total absence of gravel, of fossil stream beds, and of 
lateral uncomformities render it equally improbable that the Colob was 
deposited by fluviatile processes. The only remaining possible agent is 
the wind. We cannot yet be certain that the Colob sandstone is a 
wind formation ; nevertheless none of its characteristics seem to oppose 
such an hypothesis. The uniformity and fineness of the component 
quartz grains, the steepness of the cross-bedding, its general uniformity 
with interesting minor variations, the even truncation of the successive 
cross-bedded strata, and the tangency of the overlying layers to the 
plane surface thus formed suggest a series of great white dunes marching 
forward to the east and south from the base of the Basin Range moun- 
tains. Far to the southeast the Colob sandstone grows thinner (Ward, 
