102 National Geographic Magazine. 
already referred to; and when the rise in the level of the waters 
of the lake overtook the uplift, probably at a time of slower 
mountain growth than that which first formed the lake, the poimt 
of overflow may have been many miles to one side of its previous 
drowned-out course. The moderate elevation of the eastern end 
of the range, where it connects with the Yampa plateau, may 
possibly have then been a little higher than a point farther west, 
where the overflow was consequently located. This is perhaps 
hardly as probable as the postulates involved in arguing a truly 
antecedent course for the river; but its impossibility is not as 
strictly proved as would be necessary before a definite conclusion 
as to the continuous persistence of an antecedent river could be 
finally accepted. Such continuity of action must be rare and 
should be rigorously demonstrated if possible. 
It must, moreover, be remembered that Emmons* is of the 
opinion that the Colorado. river is not antecedent at all, but is 
superimposed on the eastern portion of the Uinta range from 
a course that it had chosen upon a sheet of horizontal sedi-. 
ments—the Wyoming conglomerate—which he supposes once 
stretched unconformably all‘over the previously deeply eroded 
surface of the uplifted range, where the cafion is. now cut. He 
quotes facts of two kinds in evidence of this ; first, the remnants 
of the Wyoming conglomerate still lie on ridges as high as those 
that enclose the river cafions ; second, the Green and certain of 
its branches possess tortuous courses, out of accord with the 
structure of the range. It might be added that the wide open 
valley of Brown’s park, in the middle of the range is best explained 
as the product of a pre- Wyoming cycle of erosion by rivers that 
were extinguished when the Wyoming beds were laid over 
the mountains. The strongest objection to Emmons’ conclusion 
seems to be the great amount of erosion that it requires ; erosion 
sufficient not only to remove the Wyoming conglomerate from 
nearly all its former overlap on the Uinta range, where it had 
buried and extinguished a pre-Wyoming drainage, but also to 
carry away a vast extension of the formation at the same height 
north of the range. It may be best to conclude that both ante- 
cedent and superimposed processes must be called on: for one 
must hesitate before admitting that the Wyoming beds stretched 
all across the country north and east of the Uinta range up to 
the height at which the remnants are now found on the range ; 
* Fortieth Parallel Survey, ii, 1877, 194, 205, 206. 
