E.NDUCH.] CRETACEOUS NO. 1. 228 



we pass, ascendiug, through the Lower Carbouiferous, then through the 

 red sandstone, and about three miles north of the conflux of Junction 

 Creek with the Animas, reach the Lower Cretaceous beds. Up to that 

 ■point the dip and strike have been conformable, but as soon as the white 

 sandstones, belonging to ls!o. 1, are met with, a change takes place. 

 Although the general dip remains the same, its angle is changed to the 

 extent of 6° to 8°. While the lowest strata show a smaller angle of dip 

 near the top of the hill on which they crop out, they dip far more steeply 

 a short distance farther south. From the point above given, on the 

 western edge of Lower Animas Park, the lineof Cretaceous outcrop runs 

 along toward the northwest,. the white sandstones always occupying a 

 position high up on the hill. They are white to yellowish in color, mid- 

 dle to fine grained, sometimes stained in spots or stripes by hydrated 

 sesquioxide of iron. At stations 42 and 43 their most northerly limit 

 is reached, and their elevated position tempted the Indians to use the 

 hills as "look-out" points. From there northward nothing but red sand- 

 stone can be found until the region of isolated trachytic eruptions is 

 reached. Almost due west of station 42, which is located upon a small 

 mass of trachyte ca^jping these Cretaceous sandstones, is the La Plata 

 group, a portion of whose volcanics covers the Carboniferous sandstone. 

 To the southwest from the station the line of Cretaceous outcrop con- 

 tinues, keeping ofi" some distance from the La Plata's. Very little varia- 

 tion is shown by the sandstones along the entire line of exposure. Below 

 they are massive, weathering in heavy, partly rounded bowlders; wher- 

 ever they form the capping of some bluff, and are of a more quartzitic 

 character they break into angular fragments. Eemains of plants, that 

 Cannot be recognized, however, on account of ver^^ poor preservation, 

 are found in them. Higher up the strata are no longer so thick -, and 

 after a thickness of 800 to 1 ,000 feet has been passed, a bed occurs, show- 

 ing indications of coal. Immediately above these sandstones the shales 

 of iSTos. 2 and 3 set in, producing, as a rule, a depression after the prom- 

 inent ridge of jSTo. 1. 



On the east side of the Animas, the conditions under which No. 1 oc- 

 curs are very much the same. It reaches the valley by virture of its 

 southerly dip opposite the point where it is reached by the same forma- 

 tion on the west side. The succession of strata is almost identical, with 

 this exception, that locally the indications of coal disappear. Inasmuch 

 as their presence is due only to particularly favorable circumstances, 

 this is by na means surprising. Here, as well as on the opposite side, 

 the white sandstones form the highest points of a series of hills border- 

 ing upon the Carboniferous strata. Toward the top, again, the single 

 beds become thinner, containing interstrata of shaly slates. On the 

 face of the bluffs east of the Animas, the nonconformability was not so 

 striking as on the west, but its existence is denoted by the difference 

 in the angle of the dip. A section taken from station 40, (Section V,) 

 in the direction of south 15° west, past station 44, will give an idea of 

 the arrangement of strata. The lower strata given in the section be- 

 long to the older formations. Lower Carboniferous beds are repre- 

 sented, a, overlaid by yellow shales containing strata of limestones and 

 sandstones, h, c, d. In these latter, Carbouiferous fossils are found. 

 Above them follows a deposit of blue limestone, with numerous Fro- 

 ductus semistriatus, e, /, g, immediately underlying the red sandstones, 

 ^, upon which station 40 was located. One prominent stratum, of 

 ■white sandstone, *, middle-grained, readily decomposing, is noticed 

 among the red, while a number of smaller layers, less important, impart 

 to the steep bluii' a variegated appearance. Upon this red sandstone 



