MB. MARVINE ON THE PARK RANGE. 27 



in late geological times. The plateau like structure of these great ranges 

 with sedimentaries dipping at high angles on their flanks, sometimes recurved 

 so as to cause inversion of the succession of strata, was a feature which 

 made a deep impression upon me in my travels through this country some 

 years ago, and in my imagination I continued the later sedimentary beds 

 in high curves over these plateaus, and dimly conjectured that tens of 

 thousands of feet had been eroded from some of the ranges, and that the 

 table or plateau like character of the ranges was due to some epoch of this 

 later denudation of the ranges when they were planed down to a common 

 level under conditions which I have explained in the volume several times 

 quoted. Such a planing down occurs when the channels of the eroding 

 streams remain for a great length of time at a general base level. But 

 when I came to study the Uinta Mountains it seemed to me that all the facts 

 which I had observed in the Park Province were duly explained by sup- 

 posing that that province had the same structure as that observed in the 

 Uinta Mountains. Since my study of that country Mr. Arch. R. Marvine 

 has made a much more thorough and careful survey of it as one of the 

 members of Dr. Hayden's corps. In the report of the United States Geo- 

 logical and Geographical Survey of Colorado, 1873, Hayden, on page 188, 

 Mr. Marvine, under the head of " Blue River or Mount Powell Group", 

 says : " The Park Range, after its abrupt rise from the broad rolling ridge 

 at the north, entirely changes in its characters. It appears to be a rectangu- 

 lar shaped mountain mass cut into the most profound amphitheatral headed 

 gorges, which are separated by the most rugged and sharp saw-like ridges 

 of rock imaginable. The main ridge lies along the southwestern side of the 

 mass, and from it the valleys and their sharp separating ridges trend in a 

 general northeast direction. The northernmost spur was composed of a 

 very distinctly and evenly bedded series of schists, gneisses, and granites 

 which had a strike nearly with the ridge, and a dip of 40 or 50 to the 

 southward. Looked at from the east, the general impression is received 

 that all of the la^ge ridges of the range have a similar structure. These 

 rugged ridges, in their easternmost portions, present a pretty uniform gen- 

 eral elevation, and as the northern ridge expands at its end into an even- 

 surfaced table-like mass of rock, the impression is given that all of these 



