OCR Text |
Show 288 arriving at the base of the mountains, where, in places, it may yet be demonstrated that these comparatively modern deposits have been suddenly tilted and more or less changed by metamorphism in the upheaval of the great lateral spurs, as instanced in the eastern flank of Great Baldj. In the shallow recesses between the outbursts of igneous activity, which threw up the gigantic masses domineering the range, these beds may extend up to the old metamorphic ridge, upon the flank of which they may rest in comparative undisturbed condition. The following profile- section ( Plate 43, Fig. 2) is introduced to show approximately the superposition of the Tertiary and Cretaceous formations as they appear in the eastern border of the Baton plateau between the Purgatory near Trinidad, and Urac Mountain south of the Cimarron, and the relation of the plateau to the Spanish range. The heavy line indicates the watershed, the dotted line showing the position of the lofty spurs diverging into the basin of the Bio Grande, the broken line the Baldy range, the lower dotted line showing the upraised western border of the Tertiary at the base of the mountains. Bespecting the mineral wealth entombed in this formation, its deposits of ooal and iron have already become famous. Besides the sections alluded to by Dr. Hayden in 1869, and those observed by Dr. LeConte and other gentlemen in different parts of the. extensive region occupied by these deposits, we are especially indebted to Mr. Morley, and later to the distinguished Dutch engiueer Herr Cornelius De Oroot, who has prosecuted special examinations in this direction with the view of developing these resources, and upon whose observations I have mainly relied for the facts relative to the occurrence and aggregate thickness of the coals here met with. The base of the formation is sharply defined from the immediately subjacent dark- gray shales of the Cretaceous by the sudden introduction of arenaceous material. This primary deposit consists of 20 to 25 feet of thin- bedded dark- brown or rusty ferruginous sandstone, upon which rests a massive bed of light- yellowish sandstone, which latter often forms precipices of 20 to 40 feet vertical. Above this occur alternations of more or less micaceous sandy shales and coarser sandstones, which, in the vicinity of the Cimarron, reach, all told, a thickness upward of 400 feet to the topmost ledges in the neighboring hills. The same association and succession of strata again appear in the valleys of the Poiiil and Vermejo, the latter of which was visited by Dr. Hayden. These sections all indicate the lower portion of the formation as the productive coal- bearing measures. The heaviest bed, which ranges from 4 to 7 feet in thickness, occurs early, though probably preceded by one or two minor carbonaceous horizons. Thus, near Mr. John Dawson's estate, at the mouth of the Vermejo Valley, the section exhibits seven beds of coal, of an aggregate thickness of 22 feet, included in about 160 feet vertical thickness of strata. At the base of this section occurs a heavy deposit of excellent coal, which is little more than 7 feet in thickness; 13 feet above this occurs a bed about 4£ feet thick, separated by thin partings; and 40 aud 20 feet respectively still higher a couple of 3- foot beds of coal are met with, the intervening strata consisting of slightly arenaceous shales, above which three 18 inch beds are found in a vertical thickness of about 65 feet. The fine under- and roof- clays associated with some of these coals often contain vegetable remains, but which generally so readily crumble on coming in contact with the air as to render it exceedingly difficult to secure specimens. Higher in the series, the sandstones afford the usual vegetable representatives peculiar to the formation, amongst which nota- |