holmes.] TKEASUEY MOUNTAIN. 67 



Mountain. The dip is at first slight, but before we reach the Lower Cre- 

 taceous, it rises to 30°. The strike is at right angles to the stream- 

 course, but turns to the south on both sides of the mountain. It appears, 

 from such examinations as I was able to make, that Treasury Mountain 

 is a short anticlinal, or oval shaped quaquaversal, that seems to have 

 been produced by some agent associated with great heat, since the high 

 degree of metamorphism of the entire series up to the Middle' Cretaceous 

 is quite remarkable. I doubt if the sedimentary measures are entirely 

 penetrated in any part of the mountain. The Jurassic and Lower Creta- 

 ceous rocks reach high up the sides of the arch, while the lines of shale- 

 outcrop are ranged around and support the base. The dip is toward 

 Eock Creek on the east and north, and toward two of its tributaries on 

 the south and west. The only place where the Paleozoic rocks have 

 been penetrated and exposed is on the east side, where the two branches 

 of Eock Creek, leaving the Cretaceous synclinal, cut directly into the 

 side of the anticlinal, passing through the Cretaceous, Jurassic, and Upper 

 Carboniferous rocks, into the Lower Carboniferous, (see Figure 7;) here, in 

 a deep, narrow canon, they unite, and turning to the right the resultant 

 stream follows for some distance along the strike until it reaches the north 

 end of the oval, where it cuts its way out again into the broad depression 

 eroded from the Cretaceous shales. In passing out over the highly met- 

 amorphosed beds of the Dakota group, a splendid cascade is formed 

 with a fall of 500 or 600 feet. The sandstones of this group are so 

 greatly changed here that it would be impossible to recognize them out- 

 side of their relations to the overlying strata. They are reduced to a 

 verv hard flinty quartzite, greenish in color and nearly uniform through- 

 out. The shales above are much hardened, and the Jurassic and other 

 substrata are so consolidated as to be but a series of flinty quartzites. 

 For the sake of comparison I present in this connection, Fig. 9, two sec- 

 tions of the Cretaceous rocks, one made in this locality and the other on 

 the border of the plains. The Dakota group is everwhere the same. 

 The series of shales are almost identical, and the transitions from shales 

 to the sandstones above are as like as possible. Palm-leaves and fucoids 

 are found in the lower part of these sandstones and in corresponding 

 horizons. 



In the east the lignitic coal is found near the base of the sandstones, 

 while the anthracite coal of the West occurs 2,000feet higher. An an- 

 alysis of this coal, made by Professor Mallett, demonstrates the fact that 

 it is of fine quality. (See chapter IX, Dr. Peale's Eeport.) The seam is 

 about four feet thick, but the locality is one most difficult of access as 

 well as remote from any probable market. It certainly cannot be utilized 

 for many years yet unless the immediate region should prove rich in 

 mines, in which case it would be invaluable for smelting purposes. 



Between Treasury Mountain and the Snow Mass group there is along, 

 narrow Cretaceous valley, produced by an abrupt synclinal fold, in which 

 the strata are doubled back upon each other. The forces have so pre- 

 dominated on the east side that the beds on that side are pushed beyond 

 the vertical and lie atop of the gently inclined strata of the west side. 

 The Upper Cretaceous sandstones do not occur in this depression south 

 of Aspen Creek; we have, therefore, a double thickness of the black 

 shales in the middle of the valley, giving in all a thickness of nearly 

 4,000 feet. The shales are followed or supported on either side by the 

 older strata, in the usual order. The depression produced by this fold 

 may be followed the whole length of the Elk range, and separates it from 

 the West Elk group, producing northern and southern systems of drain- 

 age. 



