222 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



whereas the northwestern outcrops, along the San Miguel, partake more 

 of the character of the western canon country. Single ridges, extending 

 for miles along the base of the older sedimentary mountains, impart 

 to the landscape that unique appearance, that has appropriately been 

 styled " Hog- back country," Small streams or livers, cutting through 

 the ridges at right angles to their general trend, separate them into rows 

 of coffin-shaped hills, that generally have sharp crests, and regularly 

 sloping sides. Oak-brush and piiions comprise the greater portion of 

 the vegetation, rendering traveling a not altogether enjoyable enter- 

 prise. Wherever sandstones form the highest part of the hill, steep 

 slopes will be formed on the north side, by virtue of the southerly dip 

 the strata exhibit. Between the single ridges there is generally a de- 

 pression, sometimes amounting to nearly 800 feet farther out into the 

 sedimentary bluff country, of smaller dimensions, however. If the dip is 

 gentle, it becomes more so the farther the beds are removed toward the 

 south ; table-shaped bluffs are frequently formed, falling off steeply on 

 all sides, except the one parallel with the direction of the dip. As a 

 means for geognostic classification these ridges answer well. It will 

 be observed that the same strata, capping any one of them at a given 

 point, extend to either side without chaoging their relative position. 



Differing entirely from the features shown in this region, are those of 

 the San Miguel neighborhood. Instead of the hog-backs and parallel 

 ridges, the Cretaceous there forms comparatively low " flats," rising on 

 the side toward the volcanic mountains. Deep caiions, frequently in- 

 accessible to animals, contain the rivers and streams. In them Creta- 

 ceous No. 1 is mostly exposed, while the succeeding higher numbers 

 overlie it, and form either gentle, grassy slopes, or are covered with 

 young growths of tiaiber. After the mountainous region has been 

 passed, into which a bay of these Cretaceous beds extended, the bluff 

 character again appears. This, however, was beyond the limits set for 

 our work during the season of 1874. Volcanic rocks overlie these sedi- 

 mentary beds at numerous points along the western border of the 

 trachitic area, and have occasioned considerable metamorphosis. Ee- 

 garding the shape and distribution of the cai3ons, as well as the possible 

 causes of their formation, more shall be said in the course of this chap- 

 ter. Without a comprehensive knowledge based upon the observations 

 made over a very large extent of country, all conclusions must neces- 

 sarily be the result of an argument based upon insufficient premises, 

 and it will not be until the entire region has been carefully surveyed 

 and mapped, that questions of the cited character cani". 3 definitely 

 answered. 



Cretaceous No. 1. 



Without the appearance of either Triassic or Jurassic, we find the Cre- 

 taceous sandstones belonging to ^o. 1 resting immediately upon the 

 red Carboniferous sandstone. Bo transitory formations whatever are 

 in sight between the two, and I am inclined to think, therefore, that 

 the Cretaceous waters of other regions invaded this, on the Animas, 

 while perhaps the land at the time was too high to be reached by those 

 of the preceding groups. From station 40, on the east side ot^ the Ani- 

 mas, the bluffs opposite present a very good section, and it was from 

 there that the relations of the different series to each other could be 

 well studied. As shown in other sections, and treated of under the 

 heads of " Devonian " and "Carboniferous," the sedimentary beds imme- 

 diately overlie the metamorphic rocks, dipping conformably with the 

 stratification the latter exhibit. Beginning with the Upper Devonian, 



