70

Fragments of iron ore were again observed strewn over the surface at a number of points to-day.

Soil and sub-soil the same as before.

Distance, 14¼ miles.

April 28.-For the first eight miles after leaving the Arroyo Pedro our road led over a gently rolling mezquite prairie, with fragments of limestone scattered over the surface, and possessing a dark, rich soil. Beyond this the country became more hilly and broken, and often cut up by deep canyons, with sides formed of precipitous walls of limestone. This limestone is of various degrees of hardness, sometimes very compact, and emitting a ringing sound when struck with the hammer, and at other times so soft that it may be crushed readily between the fingers. The width of the canyons varies from fifty to eighty feet.

About eight o'clock A.M. we attained an elevated part of the road, whence we had an excellent view of the broad and fertile valley of the Rio Grande, estimated to be about eight miles distant; and beyond this, say twenty or thirty miles, a range of mountains was dimly visible.

After traveling for several hours over a hilly and rather broken country, we reached a group of isolated, truncated, conical hills of limestone, three hundred feet high, and beyond these encountered a succession of abrupt terraces of Cretaceous Limestone, varying from one hundred to two hundred and fifty feet in height. These form the eastern border of an elevated table land that stretches irregularly for many miles in a northwesterly and southerly direction. We here struck the San Pedro, or "Devil's River," a broad stream of clear water, which winds its way through a deep and rugged canyon. This remarkable canyon is upwards of a hundred yards wide at the entrance, and presents on either side nearly vertical walls of white, gray, and yellow limestone, in nearly horizontal beds. The layers vary greatly in compactness, some of them being soft like chalk, and others extremely hard. This difference in the character of the beds causes them to weather unequally, giving to the sides of the canyon a remarkably picturesque appearance. As we advance the walls increase in altitude, and at one mile from the entrance they rise to nearly four hundred feet above the bed of the river. In some places large caverns, with arched ceilings, have been scooped out of the rock, while in others isolated sharp pointed columns are seen standing at various distances from the sides of the canyon.

On reaching, after some difficulty, the summit of the table land, we had an extensive view of the adjacent country, which exhibits evidences of denudation on a large scale. The surface is everywhere traversed by rocky canyons, some of them many yards in width; here rude, conical, flat-topped hills of limestone project abruptly to the height of two or three hundred feet; there extend long ranges of lofty cliffs, or gently sloping ridges, sometimes close together, at other times miles apart; while in the distance