283 



acter and meclianical aud chemical aggregatiou of its components. It 

 would appear highly probable that these deposits prove to be identical 

 n age and origin with similar accumulations observed by Dr. Hayden 

 n the plains bordering the foot-hills in Colorado. 



Besides these, the superficial deposits occurring in the basin proper 

 are all referable to the disintegration of the immediately subjacent 

 strata ; and these consisting in the main of the soft Cretaceous shales, 

 the soil resulting plainly bears the stamp of its origin in the extremely 

 fi-uelj-comminuted condition of its components, and which are in places 

 mixed with a greater or less percentage of arenaceous material derived 

 from the Tertiary formation. This soil supports a fine growth of the 

 l^eculiar gramma-grass, which affords throughout the year excellent 

 pasturage. The country is already occupied by many enterprising stock- 

 growers, whose herds and flocks roam the broad i)lains and are counted 

 by thousands. Along the water-courses, wherever water can be easily 

 conveyed by means of acequias for irrigation, the soil produces abundant 

 crops of corn, the cereals, and various vegetables, demonstrating its 

 fertility and the adaptability of the climate for agricultural as well as 

 13astoral j)ursuits. 



Manifestations of igneous phenomena. — Incidental reference has already 

 been made to the basaltic-capped mesas and isolated volcanic cones 

 which constitute the northern and northeastern limits of the basin, and 

 we would here refer to similar deposits and other evidences of com- 

 paratively modern igneous activity, which are manifested within the 

 limits immediately under consideration. Forming a natural boundary 

 along the south line of the district, the mesas of Eayado and Gonzalitas 

 extend far out into the plain, above which they rise a thousand feet or 

 more. The great bed of basalt with which their summits are protected 

 once plainly formed an unbroken sheet of igneous matter with that 

 lying immediately to the west, and forming a narrow belt here reclining 

 upon the granitic or metamorphic deposits, which spread over a con- 

 siderable tract surrounding the Black Mountain group, a section which is 

 intersected by mountain-ridges, marking the denuded crests of gigantic 

 dikes, the evidences of an earlier epoch of igneous activity, a mountain- 

 building epoch in contradistinction to that in which originated the great 

 basaltic mesas, and still later scoriaceous volcanic cones. It is here 

 these modern and ancient products of igneous activity are most inti- 

 mately associated ; the great Chicorica overflow being some fifty miles 

 distant from the igneous manifestations seated in the main range, with 

 the extensive plateau of the Tertiary intervening, which bears no ob- 

 served evidence of having been involved in the basaltic inundation, the 

 vestiges of which occupy so large a region to the east and south. 



While the basin of the Canadian is partially surrounded on two 

 sides by the immense basaltic-capped mesas, the flat summits of which 

 rise 1,000 to 1,500 feet above its surface, the plain itself is every- 

 where traversed by dikes, the similarity of the components of which 

 would refer them to the same age as that to which belong the 

 enormous overflow in the taVfle-lands. These dikes are of all dimen- 

 sions, the majority varying in width from 1 to 2 feet, though sometimes 

 much greater, and bearin,g, if not always, at least iu all those at pres- 

 ent known, nearly east-west. Their presence and course are plainly*dis- 

 ceruible by the low ridges of dark basaltic debris marking their outcrop 

 in the surface of the plain ; iu few instances exhibiting riule horizontal 

 crystalline structure, a fine example of which occurs near the southern 

 entrance of the Eaton Pass, which has been mentioned by ]>r. Hayden. 

 Usually, however, they present an amorphous structure in great variety, 



