226 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



backs," closely resembling those near Canon City. From there the 

 Cretaceous beds begin to slope off very gently, forming low bluffs and 

 ridges for a considerable distance. Our work did not take us beyond 

 the third ridge. The comparative scarcity of fossils in the beds just 

 mentioned is greatly to be regretted, because, with their aid, a more 

 strict classification of the strata could have been obtained. During the 

 summer of 1875, in the continuation of the geological and topograph- 

 ical work in Colorado Territory, this region adjoining the south will be 

 explored, and more careful studies of the higher Cretaceous groups can. 

 be made, than were permitted by the limited time and the plan of work 

 during 1874. 



West of the Animas the ridges, that are no longer so prominent on 

 the east side, have retained their form and relative elevation. Station 

 45 is nearly 200 feet higher than station 44, both being located on the 

 same ridge, No. 3, but the latter being nine miles further east. From 

 there onward, however, the ratio of decrease is far more rapid. The 

 sandstone forming the summit of ridge No. 2 has given protection to 

 the underlying shales to so great an extent, on the west side of the 

 river, that a number of "tables " have been formed, similar in shape to 

 those produced by a cap of basalt on some readily-decomposing sedi- 

 mentary rock. On it is located station 41, south of Junction Creek. A 

 section taken through this station, in a direction of south 30° west, (Sec- 

 tion VII.) will give an idea both of the orographic features of the local- 

 ity, and of the vertical distribution of strata. Red Carboniferous sand- 

 stone, a, again forms the lowest member of the section, underlying the 

 white sandstones, b, of Cretaceous No. 1. Analogous to the variation 

 on the east side of the Animas, a series of beds sets in, c d, comprising 

 sandy, shaly, and argillaceous sandstones. They already show an in- 

 crease in the angle of dip over that shown by the lower sandstone. A 

 yellowish sandstone, e, closes Cretaceous No. 1, immediately overlying a 

 bed of dark slaty shales, that show indications of coal. The gray shales, 

 /, of No. 2 then follow, capped by the fine-grained yellow to reddish 

 sandstone of ridge No. 2. The ridges of this sandstone are not so reg^ 

 ular here as some distance either to the east or west, Owing to the fact 

 that frequently " tables" were formed, and subsequent erosion caused two 

 ridges to remain, both capped by the same sandstone, h. Gray to green- 

 ish shales, i, corresponding to 7c, of section VI, follow this sandstone. 



This concludes the consideration of the Cretaceous area on the Rio 

 Animas and its tributaries. The formation varies but little in the ar- 

 rangement of its members from the schedule that has been long ago 

 established at other points, although in vertical development changes 

 occur even within short distances. One very interesting point was 

 studied here, the occurrence of coal. The conflicting opinions regarding 

 the age of coal-beds in a number of more easterly and northerly local- 

 ities are too well known to be dwelt upon, and it is a matter of impor- 

 tance, therefore, that its position here is established beyond dispute. In- 

 dications of it, and narrow seams, occur near the upper end of No. 1, 

 below the gray shales, containing Inoceramus and Gryphcea. Again, a 

 well-developed bed is found on the sandstone forming ridge No. 2. 

 Whether or not this bed is continuous throughout the entire formation 

 I am unable to say, but presume that where it is not actually developed, 

 indications will be found upon careful search. A third bed was found 

 by Mr. Wilson near station 45, the thickest thus far, resting near the 

 sandstone capping ridge No. 3. For miles beyond these ridges the Cre- 

 taceous beds continue in regular succession, sloping off gently in a south- 

 erly direction, so that no doubt as to the age of the coal can be enter- 



