280 



latter, the Canadiau glides into its great caiioii, aud thence, far to the 

 south, its channel is said to be walled in by precipitous bluffs of red 

 and variegated sandstone. At the entrance to the canon, the lowest 

 point in the basin, the stream has an altitude of about 5,700 feet above 

 tide- water. In the distance of forty-five miles direct, or to the confluence 

 of the Eio Mora, the stream has a descent of probably 700 feet, along a 

 part of its course but little known, and, it is believed, as yet unexplored 

 hy the geologist. Above the canon, the stream traverses a broad valley, 

 which gradually slopes from the base of the Tertiary plateau on the 

 west ; its eastern border being less uninterruptedly defined by the con- 

 fused range of volcanic hills and basalt-capped mesas, which rest upon 

 and pierce the sedimentary formations south and east of the Chicorica 

 Mesa, a shallow, triangularly-shaped basin, with an area of about nine 

 hundred square miles, its sharp angle terminating near the southern 

 foot of the Raton Pass, amidst the gorges which mark the western limits 

 of the great basaltic table-land, where the valley reaches near 6,500 feet 

 altitude. 



Dr. Hayden has already noted the peculiarities of the basin, attrib- 

 uting its origin to the erosion of the Tertiary lignitic formation, which 

 at a former time doubtless occupied the entire extefit of the valley, and 

 stretching far eastward into what is now comprised in the plains, where 

 its ancient border, if at all recognizable, is obscured by superficial accu- 

 mulations. 



Cretaceous. — This upper basin is everywhere underlaid by the Creta- 

 ceous, the upper deposits of -sn hich here consist of heavy measures of 

 shale, with intercalated thin bands of indurated and calcareous matter, 

 attaining approximately a thickness of 800 to 1,000 feet. These deposits 

 have been recognized as the equivalent of formation No. 4 of the series 

 on the Upper Missouri, and it is to their yielding nature that the gentle 

 slopes and comparatively uniform surface which characterize the basin 

 are attributable. 



In the vicinity of the Cimarron, where they exhibit the greatest verti- 

 cal extent of any single exposure in the abrupt declivity of the Tertiary 

 plateau, underlying the sandstone of that age, they afford a section of 

 above 500 feet, constituting quite half the entire elevation of these bor- 

 der hills. The deposit is here seen to consist of generally dark-blue shales, 

 the upper 190 feet being more of a grayish blue, with little, if any, arena- 

 ceous material intermixed. Ninety feet below the base of the Tertiary, 

 concretionary argillo-calcareous masses, generally of small size, are met 

 with, affording fragmentary specimens of Baculites, Inoceramus, &c. ; and 

 180 to 190 feet from the top occurs a thin band of shale, from which have 

 weathered numerous and beautifully-preserved fossils, characteristic of 

 this period. Below the latter horizon there occurs a rather marked band 

 of large concretionary masses, also containing similar fossils to those 

 mentioned above, below which, however, evidences of life are rarely met 

 with until reaching a horizon some 370 feet below the top ; and thence 

 200 feet lower occasional fossiliferous bands occur, always characterized 

 by the peculiar Cretaceous fades of their faunae. 



Between the latter point and the Canadian, twenty-five miles to the 

 east, similar shales apparently compose the bulk of the strata, with, 

 however, as we approach the lower levels, more frequent interpolations 

 of calcareous bands, which often form regular layers of blue argilla- 

 ceous limestone of a foot or more in thickness, Near Mr. Henry M. 

 Arms's (Loomis's ranch), a few miles above the mouth of the Vermejo^ 

 and near the confluence of Crow Creek, one of these thin limestone 

 beds outcrops in the base of a low outlying mound, which affords an 



