GEOLOGICAL SURVEY OF THE TERRITORIES. 125 



formed by the anticliuals and synclinals produced by the upheaval of 

 the unchanged rocks. 



All the lower beds are more or less arenaceous and of a brick-red 

 color, with only three layers of a light-gray sandstone. No fossils can 

 be found in any of the rocks, so that it is difficult to determine their age 

 with certainty. We believe that the lower beds are carboniferous, and 

 have received their red color from the sediments which were doubtless 

 derived from the disintegration of the red sienitic rocks upon which they 

 rest. It is also quite possible that a portion of the red beds are triassic, 

 and also that the yellow, gray, and rusty sands and sandstones above, 

 are Jurassic. 



Lying above the supposed Jurassic and beneath the well-defined cre- 

 taceous, there is a large thickness of sandstone which I have called 

 transition strata, because they occupy the position of the lower creta- 

 ceous, as shown on the Missouri Eiver and in Middle Kansas. These 

 beds are well developed and quite uniform in their lithological character 

 all along the mountain sides from latitude 49° to the Arkansas, yet 

 they have never yielded a single characteristic fossil that would deter- 

 mine their age. I have, therefore, called them provisionally lower cre- 

 taceous, or beds of transition from one great period of geological history 

 to another, and the characters of the sediments which compose them 

 justify the name. 



Near our camp on the Big Laramie, which was about thirty-five miles 

 southwest of Fort Sanders, and about fifteen miles above the foot of 

 the hills, are some singular illustrations of the dynamics of geology. 

 On the southwest side of the stream, and inclining eastward or south- 

 eastward, the entire series of red and variegated beds are shown in their 

 order of succession one thousand five hundred to two thousand feet in 

 height. At the foot of this escarpment is a low ridge of the red material, 

 which is so grassed over that the connection with the sienitic nucleus can- 

 not be seen. This covers a belt of sienite about two hundred yards 

 wide and three to five miles long, the jagged masses of rock reaching a 

 height of one thousand feet or more, and standing nearly vertical or 

 dipping slightly to the southeast. Between the sienitic beds and the 

 river are the two low ridges of cretaceous Nos. 2 and 3, which seems to 

 have been lifted up with the sienite, but to have fallen back past a ver- 

 tical position, so that they now incline from the sienite ridge, while on 

 the opposite side the beds have a regular dip from the ridge. This pecu- 

 liarity seems to be common in various localities, owing to the fact that 

 the metamorphic beds which compose the central portion of all the moun- 

 tains have suffered upheaval, prior to the deposition of the unchanged 

 beds. Therefore, in the quiet elevation of the mountain ranges, the 

 beds are merely lifted up in the direction of the dip of the older rocks 

 on one side, while they are, as it were, pushed away from the opposite 

 side, forming what may be called an abrupt or incomplete anticlinal. 



On the opposite or south side of the river there is a gradual slope of 

 two thousand feet above the bed of the stream, the strata inclining 5° 

 until we reach the nucleus of another mountain range; so that we have 

 here, as it were, two huge monoclinals. These monoclinals form local 

 anticlinals, inasmuch as, in some places, all the beds incline for a short 

 distance from a common axis. 



On the north side of the river, and east for ten to twenty miles, the 

 flanks of the mountain ranges are covered with the unchanged rocks, 

 which give comparatively gentle grassy slopes, owing to the readiness 

 with which they yield to atmospheric agencies. Through these slopes 



