402 Mountain Upthrusts. 
of each of which were determined by the successive changes in the 
configuration of the land-surface, as elevation and degradation 
progressed. 
Again, although the Archean rocks are theoretically represented 
in that section, they have not been brought to view in the axis of 
the fold, because even the immense erosion which the uplifted strata 
have suffered has not been sufficient to reach them there.! There- 
fore, in estimating the amount of vertical displacement which has 
taken place in the Uinta fold, I have reference only to the formations 
from the Uinta Sandstone to the Laramie Group (inclusive). 
Now, referring to the foregoing table, we find that the minimum 
thickness of these formations aggregates twenty-three thousand eight 
hundred feet. Add to this five thousand feet for the height above 
the level of the sea at which the lowermost strata of the Uinta 
Sandstone have been observed, and we have an aggregate of twenty- 
eight thousand eight hundred feet. The evidence seems to be con- 
clusive.that the elevation of the fold began immediately upon the 
close of the Laramie period ; and it is confidently assumed that none 
of its strata were then much if any above the level of the open sea. 
Hence the conclusion that the full amount of vertical displacement 
in the Uinta fold has not been less than twenty-eight thousand eight 
hundred feet. 
The evidence derived from a study of the great fold seems also to ` 
be conclusive that its elevation was continued between the close of 
the Laramie period and the close of the Tertiary ; and other evi- 
dence is equally conclusive that continental elevation was continued 
during the same time. That is, it is assumed that the orogenic 
movements which have resulted in *he production of the Uinta and 
other mountain-making folds were approximately synchronous in 
their origin and coeval in their duration with the epirogenic” move- 
ments by which the great continental area upon which those folds 
now rest was raised to its present elevation above the sea.* 
1 Archsean rocks are exposed within a limited area upon the northern 
side of the fold; but they were evidently a part of an uplift which was 
older than the fold. 
2 Etym., Hze:pos—mainland, or continent. 
3 Certain epirogenic movements must necessarily have taken place to 
form the barriers by which the Laramie sea was cut off from the ope? 
oceans. Local unconformity among the Laramie strata which has been 
observed near the top of the group in Southern Wyoming indicates that 
. certain other premonitory movements took plate before the Uinta es 
was well defined: 
