Page:Memoir of a tour to northern Mexico.djvu/136

[ 26 ] Having crossed the Arkansas, I met with the first rocks again, on the "middle springs of Cimarron," (468 miles;) it was a sandy limestone above common sandstone.

Six miles west of the Crossing of Cimarron (500 miles from Independence,) light bluffs rise in the prairie, of a yellow, reddish, and spotted sandstone, combined with lime and argile.

A few miles beyond them a large, isolated mountain of boulders stands in the plains, composed of heavy blocks of quartz and quartzose sandstone, and maiy erratic rocks were afterwards found on our road.

On Cedar creek, McNees' creek, and Cottonwood branch, a yellow sandstone prevailed.

On Rabbit ear creek I met for the first time with amygdaloidal basalt, a black, heavy, basaltic rock, with a great many irregular, vesicular cavities, that are generally hollow—sometimes, too, filled with lime; in rare instances, with olivin. This rock is most common throughout the high mountains of Mexico. It occurs in most irregular masses, in whole mountains, as well as in millions of pieces strewn over the surface of the country. Here it rose in high perpendicular walls, as bluffs of the creek, and a very compact quartzose sandstone was below in horizontal layer.

The Round mound, a mountain in the prairie about three miles further wert, which I ascended, is formed of a brown, decomposed basaltic rock.

On Rock creek, and Whetstone creek, the amygdaloidal basalt with underlaying sandstone was found.

In going from there to "Point of Rocks," (600 miles.) extensive strata of a yellow, compact quartzose sandstone are passed, dipping gently towards the east. Point of Rocks itself, a spur of the western mountains, is a mass of sienite.

Some 12 miles beyond it, rises a hill in the plains, composed of very compact, black basalt, with underlaying white sandstone.

The bed and bluffs of the Rio Colorado and Ocate creek (627 miles,) are formed by quartzose sandstone.

The Wagon mound, an isolated mountain in the high plain, consists of a compact, black, and spotted basalt, rising in columnar shape.

On Wolf creek (664 miles) the amygdaloidal basalt and quartzose sandstone reappeared, both in horizontal layers.

Reaching the Gallinas creek, near las Vegas, (690 miles.) I met, after a long interval, with limestone again. It was a dark blue, with casts of Inoceramus of the cretaceous series.

From here we penetrated into the very heart of the mountains. At first we met but with sandstone, common and quartzose, and of most different colors.

Near San Miguel (707 miles,) a coarse conglomerate was found of decomposed granite, sandstone, and lime, and large blocks of decomposed granite lined the Pecos river, opposite the old Pecos village, (737 miles.)

In the cañon leading from here to Santa Fe,at first sandstone is found, common, quartzose, and calcareous, of various colors and granulations, tilt about 15 miles from Santa Fe, granite in situ appears, and continues all the way to Santa Fe. Near where 1 met for the first time with granite in situ, the sandstone, if I may judge from a very limited examination, was suddenly uplifted and thrown back in an angle of nearly 100 degrees.

West of Santa Fe, granite seems also to prevail. In my excursion to the Placers, southwest of Santa Fe, I found sandstone below, and on the height of the mountains granite and trap rocks.