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Show 109 Local geology.- Proceeding from the Rio Grande at Santa Glara toward Baldy Peak, we first cross the soft Tertiary beds, sands, clays, and marls, fonning a nearly perfectly barren stretch, especially between Pajoaque and San Juan, and yielding much to erosive influences, whereby many narrow gnlleys, and here and there peculiar architectural forms, are produced. In these beds, near Ildefonso, I made some excavations in 1873, while on the way to Fort Defiance under your expedition, ( division %) and brought to light fossil bones of a mastodon, only ono of them perfect, however; others were broken and yielded but fragments. Unfortunately I had but one day for this work, but in 1874 Professor Cope made more extensive excavations while attached to this expedition. He succeeded in discovering many precious treasures in the line of Tertiary fauna. Only one spot appeared to promise results. I searched in vain all the way from Pojoaque to San Juan in the fall of 1874, when passing again through this region. Leaving these beds, and proceeding eastwardly toward the mountains, we crossed, before reaching their base, a bed of rounded pebbles and detritus of the Azoic rocks of the mountains. About five miles above the Indian town Nanib6, theRito Pojoaque emerges from a deep, narrow valley in which the Carboniferous strata are exposed, but for only a comparatively short distance, the Azoic rocks, principally granite, predominating here as well as in the cation of the neighboring Rio Tesuque and Santa ¥ 6 Creek. The Rito Tesuque is formed by three head- streams that unite far up in the mountains, about fifteen miles above the Indian town Tesuque. These head- streams are all hemmed in by narrow, well- timbered valleys, that turn, with larger or smaller interruptions, into canons. One and a half miles below the junction of the first two of these streams, which occurs in a oharminjg little mountain valley, the Vallecito, comes in the third branch from a narrow gorge in the granite rocks, and about two miles below this junction two other side canons* come in, but at the present day no water flows, in them. The granite in the northern of these side cafions is of a very coarse texture and has the white mica ( muscovite) as a constituent. In the numerous fissures of this rock is a coating of shining oxide of iron, producing an appearance seldom seen. It may have been deposited by the waters of a former iron spring. It is a fact that some prospectors in Sauta Fe" took this red substance for cinnabar, and the silvery- looking particles of muscovite for mercury. Several miles farther down the river is the Carboniferous limestone with au abundance of Prodttotua and Spirifer. These beds rest directly and conformably on the Azoic rocks. Between the Rito Tesuque and the Santa F6 Creek is a series of high and steep ridges composed chiefly of granite. Where the Santa Fe* Creek emerges from the foot- hills of the mountains stands the city of Santa ¥ 6. The chief rocks north of this locality are the Azoic- gneiss and granite- while Carboniferous limestone is found in some of the neighboring cafions, . and toward the south more recent formations up to the Cretaceous. Along the road from Santa ¥ 6 to L » & Vegas is passed, first, gneiss, then a conglomerate, and afterward Carboniferous and Triassic beds near the Pecos River, next} upturned sedimentary rocks for a long distance until we reach the level beds of the Cretaceous at Las Vegas. This road, however, describes large curves. The direct trail is much shorter, but leads across so many steep slopes that vehicles caunot make use of it. This trail leads up the Santa ¥ 6 Creek about ten miles, ascends a steep, barren declivity, some 2,000 feet in height, and crosses another deep valley before it reaches the Macho Creek, a tributary of the Pecos ; thence it leads up the Pecos some distance and over another steep declivity to the valley of the Vaca Creek and to the headwaters of the Gallinas Creek. In the valley of the Santa ¥ 6 Creek the gneiss is accompanied by primitive clay- slate and syenite. Veins of fine- graiued gray gneiss occur in a coarse aplite or granulite, also intersected by syenite seams. These singular features are nicely exposed in the rocks borderiug the river some five miles above Santa Fe\ Farther up, some curiously-shaped huge rocks are seen projecting from the sides of the canon; one of these is called " Bear rock," from its shape, resembling that of a bear. In the canou of the Macho Creek we again meet the Carboniferous limestone, which is in sight until we reach the junction with the Pecos, and from there to the top of the next ridge, on the eastern side of the Pecos Valley. Here the lithological character of the underlying granite is quite different from that west of the Macho Creek. It forms a fine- grained mixture of white feldspar and quartz, in which little spot- like aggregations of biotite are segregated. In the valley of the Vaca Creek, immediately east of that ridge, talcose schist and syenite are exposed, upon which the Carboniferous strata rest. Taking thence a northeasterly course to the headwaters of the Gallinas and Tecolote, we have to ascend another high, steep ridge, whose summit is fully 11,000 feet, and whose very top is covered with Carboniferous limestone. This fact, contrasted with the entire absence of such strata on the ridges and higher portions of the ' range west of the Pecos, appears to indicate that it was lifted after the deposition of these strata from the sea to this great height, while the Santa ¥ 6 range was in existence long before. This lifting to the present height, however, was not accomplished by one effort. Another exertion was made during the Cretaceous, as the belt of upturned Triassic and Cretaceous strata along the southeastern foot- hills of the range seems to testify, while no upturned ridges are observed on the western side of the Santa Fe* range. |