| OCR Text |
Show 63 of a soft and shaly character, frequently of a dark color, and resembling those of No. 2 ; these are the Fort Pierre group No. 4. The brown and yellow beds of No. f ( Fox Hills group) lie upon these. They are arenaceous and of various degrees of hardness, and frequently heavily bedded. Occupying a horizontal position on Cretaceous No. 5, there is found in Central Colorado a series of yellow and brown arenaceous mud- beds of estuary and fresh- water origin, which contain beds of lignite and abundant remains of the land- plants and animals of the surrounding continent. These are the Fort Union group of Hayden, or Cretaceous No. 6 of the writer. The sncceeding formations are lacustrine and Tertiary ; the earliest, or Eocene, appearing on the western side of the mountains, while on the eastern Bide this formation is omitted, the Miocene lying immediately on the Cretaceous. The hills bounding the valley of the Arkansas at Pueblo consist of shales of Cretaceous No. 4. When long exposed they become white and hard, bnt when first exposed are usually of a dark color. At Pueblo I observed scales of physoclystous fishers ( t Beryx) with Inoceramus and plant- remains. Similar remains have been drawn up from well- shafts sunk several miles south of Pueblo, and appear in the sides of ravines near the Saint Charles Creek. Tbe bluffs of the Saint Charles are 150 feet in height, and are composed of the same material, which on exposure is light- colored, and splits up into large flakes, which exhibit couchoidal fractures, and a hard consistence. Farther southward, bluffy ledges extend at right angles to the mountain- axis, facing the south. On the south side of the Greenhorn they are overlaid by a soft buff sandstone which forms the high ground, dipping 30c southeast. This is perhaps to be referred to Cretaceous No. 5. The beds of No. 4 constitute the surface of the country for a distance of from six to fifteen miles from the mountains as far south as the Grena-res Creek. One mile south of this point, the soft rusty and gray sandstone of No. 5 caps the bluffs to a height of 150 feet; No. 4 disappearing beneath it with a southerly dip. Twelve miles north of Howard's, some bluffs to the west of the road face the east; the upper 40 feet is of yellowish shade, the lower of a bluish color, 40 feet to the base. At the line of junction of these colors, the rock is filled with Ostrea congesia and fragments of Haploscapha. At Howard's, on the Huerfano, the mesas are composed of No. 4, lying nearly horizontal in shaly argillaceous layers of a muddy color. The mesas are 50 feet high; wells sunk 50 feet from their foot- level exposed the same rock of a darker color to blackish, containing Ammonites, Baculites, and Inoceramus, A boring of 30 feet from the bottom of the well brought up the same material. The tract of country between Pueblo and the Huerfano is elevated, and has an arid appearance, owing to the scarcity of water. The valleys of the streams flowing from the westward are exceptions to this statement, and toward the foot of the mountains beautiful meadows and farms can be seen from the line of the road. Turning toward the mountains at Howard's, we proceed up the valley of the Huerfano, with nearly horizontal beds of the buff sandstones of No. 5 exhibited on the south side of the creek, to near Badito, near the point of extinction of the Wet Mountains. Here the beds are observed to rise to the mountain- axis, and are displayed in the following order, beginning with the lowest: The red beds display their brilliant color high up, and are overlaid by the bed of snow- white gypsum, usually referred to the Jurassic. Above this we have the sandstone of Cretaceous No. 1, constituting an important topographical feature of the mountain- slope. The valley below is doubtless excavated from No. 2, while outside of it a low hog- back of siliceous brown limestone of Cretaceous No. 3 runs parallel to the range near the village. The light and dark shales of No. 4 form the ledges outside of and above No. 3, constituting the faces of the bluffs on the north side of the Huerfano Valley. All of these beds lie at an angle of 45° east at the line of strike; but the soft sandstone, which caps No. 4, and which I have called No. 5, has been little disturbed. From the hog- back exposure of No. 3, I obtained twelve species of fossils, as follows: Ostrea congesta; Ostrea near larva, Mort.; a shell with a ribbed disk; Inoceramus; a Pecten; Piychodus Tlhippleyi, Marcou; Ptychodus papil-lo* us, Cope; GaleocerdoEdgertonii, Agas.; Otodus, two species; Lamna Texana, Roein.; Lamna, No. 2 ; Oxyrhina, sp. The sandstone bed of Cretaceous No. 1 forms the slope of the southern extremity of the Wet Mountains. It dips east, south, and west as the road passes over the ridge and enters the valley, separating that range from the Sangre de Cristo Mountains, which is known as the Huerfano Park. On the west side ot the Wet Mountains the sedimentary rocks repeat with reversed dip the arrangement seen on the eastern flank. The red beds and the gypsum are conspicuous landmarks high above the valley, while the sandstones of No. 1 are seen to be immediately overlaid by light-colored shales, which greatly resemble those of No. 4, but which are as much like those of No. 2. These beds and those below ihem through the red Trias, are exposed along the road at one point of its passage of this anticlinal. The plain of the Huerfano Park is occupied by mesas of a soft yellowish rock of Cretaceous age, but of which of the subdivisions of the latter I did not ascertain. The eastern slope of tbe Sangre de Cristo Mountains, as well as the foot- hills traversed |
