224 GEOLOGICAL SURVEY OF THE TERRITORIES. 



again follows, 1c, n, separated by a bed of blue limestone, m. Besting 

 directly upon the Carboniferous strata, we find the white sandstones, 

 o, p, of the Lower Cretaceous. Analogous to the occurrence on the west 

 side of the Auimas, the beds become thinner; above that the color 

 changes, turning slightly yellowish, and shales appear in the yellow 

 sandstones, q. A stratum of white sandstone, r, follows, at the upper 

 end of which coal is sometimes observed. In regular succession the 

 shales and sandstones of higher numbers occur. No. 2 is represented 

 by dark-gray shales, s, frequently carved into beautifully regular forms 

 by erosive agents. Owing to the smaller resistance they offer, they are 

 generally found to present steep slopes on the north side, and are worn 

 away to the bottom of small, narrow valleys, which owe their existence 

 to this circumstance. At some points the gray color changes to a 

 muddy yellow in certain strata. Ascending the steep slope produced 

 by these shales, a yellow sandstone, t, is reached, forming the crest of 

 a long-continued ridge. Between this, t, and the succeeding series of 

 shaly sandstones and shales, u, a bed of coal was found, varying in 

 thickness from two to five feet. A solid yellow saudstone, v, overlying 

 the series mentioned, caps another bluff of considerable extent. 



The outcrop of the Lower Cretaceous runs along approximately par- 

 allel to that of the Carboniferous, about eight miles south of it. Prom- 

 inent points rendered conspicuous by their white or light-yellow color 

 denote its course. On Bio Florida it reaches down nearly to the stream. 

 Near the Binos it makes a curve to the southeast, and was lost out of our 

 field of work. 



Cretaceous JVb. 2. 



All along the line of the " first ridge," which is formed by the divis- 

 ion that has just been described, a valley is observed, containing streams 

 of some size. Junction Creek on the west side and a portion of the Florida 

 on the east run in this valley. Its formation is due to the presence of 

 the shales of Cretaceous No. 2. Traveling up the former, steep bluffs 

 will be seen on its south side, composed of dark-gray shales, subject to 

 considerable erosion from the action of water. Of fossil remains but 

 few were collected in these shales — fragments of Inoceramus and of a 

 Gryphcea species. They are characteristic of the horizon, however. Be- 

 maius of plants occur, but sparingly. From Junction Creek southward 

 the valley the Animas widens out locally, and here the shales of No. 

 2 are again found. Sometimes they form narrow spurs, running out 

 from the higher bluffs. A capping of sandstone protects the ridges 

 and bluffs farther west from erosion. Throughout the region the 

 higher numbers of the Cretaceous dip in the same direction with No. 

 1, but it will be observed that the angle of dip is somewhat increased. 

 It is a constant feature, and apparently not owing to the pinching out 

 of any one or the other stratum. Why this should be so is not very 

 clear, unless a gradual settling and consequent consolidation of the 

 shaly strata of No. 2, which reach a thickness of 400 to COO feet, should 

 have been able to produce the result noticed. In the sandstone capping 

 the bluffs and ridges, small fragments of Inoceramus and remains of 

 plants were found. As the ridges of that section of country are so very 

 regular in their occurrence and course, I have numbered them for the sake 

 of greater convenience. The one protected by this yellow sandstone is 

 " ridge No. 2." East of the Animas the same features may be ob- 

 served. Frequently the ridges are cut transversely, but their connec- 

 tion is evident. On the Florida, a short distance west of station 47, a 

 curious phenomenon was noticed. Station 47 is located on ridge No. 2, 



