It was not in my power to explore this range to the south, but I was informed by persons worthy of confidence, that throughout its whole extent, as far south as the parallel of Mazatlan, it was utterly impassable for wagons, and there was no possibility of finding, south of 31° 20′, a line for a railway. The report of its impracticability for wagons was confirmed by the fact that the Camino real, (highway,) established by the Spaniards to connect Chihuahua and Guymas, makes a great circuit, and passes to the north of 31°.20, and within what is now the territory of the United States.

This stupendous range of mountains, which drops so abruptly a few miles north of the boundary, as if to make room for the highway which is to connect the Pacific and Atlantic States, no doubt, reappears to the north, in the neighborhood of the Gila, but our information is not yet sufficient to establish the connexion. I am quite satisfied of one thing, however; its equivalent is not to be found in what is called the Sierra Madre, in New Mexico.

Pursuing our course still eastward, we pass over wide plains bounded by detached ranges of mountains of metamorphic and other limestones, associated with igneous rocks, rich in silver and lead, and at El Paso we encounter the western flank of the third great mountain chain, the Rocky mountains, known in that particular locality as the Organ mountains; and at intervals of about eighty miles we cross two other ranges, the Eagle Spring mountains and the Limpia range of mountains.

The view will give a very good idea of the appearance of the Organ mountains in the distance, and of the Great Mesa, which reaches far away to the west. It is from the bed of the Rio Bravo, just above the gorge, where the river breaks through the range at El Paso.

These three chains of mountains appear to be spurs of the Rocky mountains, and are characterized by the presence of carboniferous limestone, greatly disturbed by igneous protrusions of what Professor Hall characterizes as of "comparatively modern origin.'

And throughout this whole region, the carboniferous and metamorphic limestone is not unfrequently traversed by rich seams of argentiferous lead ore. Between the San Luis range and the Organ mountains, the first of the Rocky mountain range, the metamorphism of the rocks is so complete and the irruptive lines so frequent, and protrusion above the crust of the earth so detached, it is impossible to say, with our present information, where the one begins or the other ends, or whether they do not all belong to the same system.

It is between these two ranges, upon the banks of the Janos river, that we discover the first evidences from the west of that vast cretaceous formation which has been traced from the 108th to the 101st meridian of longitude, and as far north as the Great Salt Lake, and south to the 25th parallel of latitude.

The western limit of this formation, discovered by the boundary survey, is the basin of the Janos river in Chihuahua, and its easternmost limit San Antonio, in Texas. How far it extends north and south has never been ascertained, but it has been traced in one direction as far as the Big Salt Lake of Utah Territory.

Granite, and its associated gold-bearing rocks, occur sporadically throughout the Rocky mountain chain, and its spurs; but the distinguishing feature, in an economical point of view, is the prevalence of carboniferous limestone, with which is found associated argentiferous galena.

Silver mines of richness have been discovered, and some of them worked to a limited extent, in the mountains about Tucson, at Barrancas, Presidio del Norte, Wild Rose Pass, in the Organ mountains, and other localities, accounts of which will be found elsewhere.

Gold mines have been worked at the Calabasas, on the Santa Cruz river, and in the mountains of New Mexico, on both sides of the Rio Bravo.

It will not be extravagant to predict the discovery of many localities where silver mines can be worked to advantage throughout the whole region where carboniferous limestone exists, extending on the line of boundary from the great bend of the Rio Bravo, in Texas, to the meridian of the San Luis range. Should this conjecture prove true, we shall have then, in abundance, the only commodity in which we are now deficient, and for which we are at all dependent upon any other country.

Another argentiferous region of exceeding richness, and, I think, one wholly disconnected from the other, is in the basin west of the Santa Cruz river, between that river and the Gulf of California. Veins of metal were discovered traversing a coarse sandstone, which will be more particularly referred to in Chapter VI on that section of the boundary.

I have stated that the eastern portion of the continent, with which we are familiar, is entirely different in its physical geography from the western, and among the distinguishing features of the first is the Appalachian chain of mountains, which sheds its waters clear from the summit to the ocean; that is to say, water once above the surface at any point, continues to flow in that position until it reaches tide-water.

Between the two great chains, which I have attempted to describe, occupying the western. portion of the continent, there are other chains of mountains, so numerous that it is impossible to describe them by words; some are continuous, some are detached ridges, others isolated peaks, rising from the plateau almost with the uniformity and symmetrical proportions of artificial structures. Between them are found basins, which have no outlets to the ocean, but are the receptacles of the drainage of the surrounding water-sheds. Of these, the most extensive is the Great Salt Lake in Utah Territory, and the most remarkable for its historical associations and present importance is the valley of the city of Mexico.

These successions of basins form a prominent feature in the geography of North America, extending two-thirds its length, and quite one-third its breadth. They belong to what has been appropriately designated as the Basin system of North America.

Those found near the boundary are Santa Maria, Guzman, and Jaqui-all to the south of the boundary, and within the limits of Mexico. The first is fed by the waters of the river Santa Maria, which runs in a northern direction, and Guzman by the river bearing the several names of Casas Grandes, San Miguel, and Janos, the general course of which is also from the south to the north; and the waters of Lake Guzman and Lake Santa Maria are said to unite in seasons of unusual freshets.

The waters of the Rio Mimbres, near the same meridian as Lake Guzman, which take their rise near the Santa Rita del Cobre, run towards that lake, but they disappear in the plain to the north of the boundary, before reaching it.

The waters of these lakes, or inland seas, are brackish at all times, but in seasons of drought, which last two-thirds of the year, they become salt, and wholly unpalatable. Their shores are covered with lacustrine deposites, and are usually unsuited to cultivation. The waters of these vast basins are not all locked up, however, by the mountains. Three great rivers, with their tributaries, have made their way in different directions to the ocean, cutting, in their passage, gigantic chasms in the mountains. These rivers are the Columbia, the Colorado of the West, and the Rio Bravo. Another river, the Gila, drains this plateau, cutting the mountains nearly at right angles, which, although a tributary of the Colorado, joins it near its