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Mountain Upthrusts. 399 
Now it happens that the region cleared by the ancient inhabi- 
tants has a tough clayey soil of such a nature that it bakes dry and 
hard in the dry season ; grass and weeds dry up, and young trees 
that would germinate in the wet season are as regularly killed in 
the dry. These Sabanas show numerous ancient remains; and 
these and also the pine forests deserve to be thoroughly examined 
by archæologists. Much might be learned to shed light on the 
studies already made on the more modern ruined cities and sculp- 
tured temples of Central America. 
MOUNTAIN-UPTHRUSTS. 
BY CHARLES A. WHITE. ! 
ERTAIN of the mountain ranges of the western portion of our 
national domain exhibit in a clear and striking manner the 
evidence that they have originated in uplifted folds of the earth’s 
crust. One of the simplest and most characteristic of these orogenic 
folds is the one in which the Uinta Range of mountains originated. 
Other uplifts of a similar character have occurred, but which, 
having been of limited longitudinal as well as lateral extent, have 
resulted in comparatively small clusters of mountains, and not in 
mountain ranges proper. The Black Hills of Dakota have originated 
in one of these circumscribed uplifts. 
In Northwestern Colorado two uplifts occur which, so far as the 
character of the displacement and of the formations involved are 
concerned, are similar to those which have just been referred to ; 
but they have occurred within such narrow limits, respectively, that 
they have each resulted in only a single mountain. The limits of each 
of these uplifts are so sharply defined, and the amount of vertical 
displacement of the strata involved is so great, that I have designated 
them as Upthrusts 
A description of these upthrusts is the special object of this article. 
But as they are structurally connected with the great Uinta fold 
and with other neighboring displacements, it will be necessary to 
devote a considerable part of it to their description also. 
1 Published by permission of the Director of the U. S. Geological 
Survey, The substance of this article will be embraced in one which is 
to appear in his Ninth Annual Report. 
