MALE.] 



GEOLOGY SECTION NO. 10. 221 



At this place is a considerable deposit of iron not noticed in the springs. 

 For some distance about the springs there is an efflorescence of salt and 

 alkali. The principal constituents of the water are common salt, sul- 

 phur, iron, and carbonates. Southeast of the butte, at the base of 

 which we find these springs, is a double-topped butte, which 1 found to 

 be composed entirely of granite. The rock was somewhat covered, but 

 I consider it to be a remnant of a line that once extended northward, 

 and that the rocks probably incline to the southwest or to the northeast. 

 The whole southern end of the park, as I learn from the notes of Mr. 

 Taggart, is volcanic. The Platte liiver for some distance follows a 

 course very near the line between the trachyte and the sedimentary 

 formations. On this line are several buttes, on the northern end of 

 which are granite outcrops, while the rest of the butte is either trachy tic 

 or basaltic. 



Following the river up from the caiion we find that it flows through 

 schists for about five or six miles. We then meet with trachyte, 

 which at this point is found on the south side of the river. As we near 

 the salt-works we find numerous isolated buttes of trachyte, many of 

 them having a conical shape. A line of these buttes extends from the 

 Little Platte, about eight miles above its mouth, toward the southwest. 

 They mark the limit of the volcanic rock in this direction. The Little 

 Platte forms the boundary from the mouth up for eight miles. The 

 main river for about eight or ten miles above the mouth of the Little 

 Platte flows in the axis of a synclinal fold, the same to which I have 

 several times already referred. The fold is here much broader than at 

 the head of Trout Creek, where we first observed it. Above the mouth 

 of Trout Creek, the Platte River cuts through the beds after being for 

 some distance on a monoclinal valley in the red-beds. Above, at Fair 

 Play, its course is again, across the strike of the beds. Here it has cut 

 deeply into deposits of gravel, which are probably the result of glacial 

 action. This may also account for the course of the stream at this 

 point, as its bed may have been determined by a glacier. Near Fair 

 Play, the gravel, which is auriferous, is from 70 to 100 feet thick, com- 

 posed of rather large rounded boulders. Between the Platte River and 

 the mountains that form the western boundary of the park, the country 

 is rather uniformly level, and so covered with drift that we have very 

 few exposures of rocks. It is not until we reach the Little Platte, about 

 ten miles south of Fair Play, that we have any definite exposures. At 

 this point, near a bend in the creek, I made the following sections, sec- 

 tion No. 10 being made at the point A in Fig. 2, Plate VI, and section 

 No. 11 from the point B to C. The dip of the beds on the bluff where 

 section No. 10 was made is about south 75° west; angle of inclination, 

 250 to 30°. 



Section No. 10. 



In ascending order: 



a. 1. Pink sandstone ( -o 



2. Space covered up / 



feet. 



3. Blue limestone, 3 to 4 feet ) 2i feet 



4. Space covered up j 



5. Reddish sandstones 120 feet. 



6. 'Space probably filled with alternation of sandstones and 



limestones 120 feet. 



7. Blue limestone 4 to 5 feet ) qq ^^^^ 



8. Space covered up . i 



