On entering the sand-hills from the north, we first pass over a considerable swell of limestone rock, from the southern slope of which we pass at once into the hills of sand. Its surface, at first variously scattered with arid shrubbery, becomes as we proceed almost pure drifting sand, blown by the wind into varying ripple-marks, and assuming all the different shapes of drift and hollow imaginable. As the view of the surrounding country becomes shut out, there is presented an exact picture of the sandy dunes on an exposed seacoast, and it seems almost strange not to hear the roaring of the surf, or catch a view from the highest elevations of a wide ocean expanse. The greatest height of this formation is on the southern side, or in the convexity of the arch, which terminates with a somewhat abrupt face, merging into the shrubby plain below.

Our route from this point leaves the Chihuahua road, passing more to the west, and thence skirting along the base of jagged mountains, forming a broken range to the south and southwest. The plain traversed is similar in character, and continuous with that on the opposite side of the sand-hills, having, however, an increased elevation. Our route, bearing S.S.W., is interrupted by occasional spurs of limestone rock, proceeding from the adjoining mountains to the south.

This character continues for some twenty miles, when we begin to notice an obvious change in the external features of the country. The frequent valleys leading from the broken mountain range on our left acquire a more fertile character, and, being removed from the incursions of drifting sand, support a richer growth of plants. Beyond this, the country spreads into wide basin plains, presenting to the eye an uniformly smooth outline. The soil is composed of a stiff clay sediment, and is occupied exclusively with a growth of coarse grasses. In their lower depressions these extended plains frequently present a perfectly bare surface, destitute of all vegetation, the retentive soil either holding the product of recent rains in wide, shallow pools, or more often showing a surface cracked and blistered under the influence of an arid atmosphere. We find frequently scattered over its surface recent land shells, as indications of its lacustrine character. In certain localities these lower depressed flats are covered with a white saline efflorescence, resembling at a distance sheets of water, to the frequent disappointment of the thirsty traveller. The roads leading over these tracts are firm and excellent. The natural supplies of water are very inconstant, being in great measure dependent on rains.

Our road hence, for a long distance, traverses a succession of these plains, of greater or less extent, alternating with short ridges, occasioned by the passage of an irregular mountain range. These ridges present along their line of elevation various depressions, at which the passage is generally accomplished by an easy gravelly slope. The exposed rocks are of carboniferous limestone, associated with various igneous products.

This character of country continues till we reach the first flowing stream yet encountered on our march from the Rio Grande; this is the Rio Sta. Maria. As here exhibited, it shows a flowing brook of limpid water, from 10 to 20 feet in width; at the crossing knee-deep, and flowing over a pebbly bed. Its source lies far to the south, in the State of Chihuahua; thence flowing north, it empties, about 30 miles from our place of crossing, into Lake Sta. Maria. This lake is shown, by the examination of the boundary commission, to be in close proximity to the larger Lake Guzman, from which it is separated by a range of mountains.

These lakes, though thus separated, belong to the same general basin, receiving the drainage of a large tract of country-the San Miguel and its tributaries entering on the north, and the

Sta. Maria on the south. The waters of these lakes having no outlet, are strongly impregnated with saline substances, so as to be unfit for drinking.

The adjoining mountains on our route are of igneous character, being composed of vesicular and amygdaloid trap, forming more or less continuous ridges, ranging north and south.

Associated with the fact of running water in this region, we see the country characterized by an unwonted appearance of fertility and verdure, not alone confined to the immediate borders of the stream, but extending over the hills and plains adjoining.

Our route, after crossing the Sta. Maria river, takes a course S. 70° W., (mag.,) passing over country characterized as above, bounded by mountain ridges of less height above the general surface than those before passed. The greatest development of mountain range lies to the west. The various rock exposures exhibit most abundantly forms of amygdaloid trap; more rarely we meet with local exposures of limestone strata, or variable metamorphic products. Conspicuously in view in our direct course are the mountains in which the silver mines of Corralitas are located, consisting of an assemblage of rounded and peaked summits of various heights, rising from 500 to 1,500 feet above the adjoining plain.

These mountains occupy an area of about 5 miles in length from north to south, and 2 to 3 miles in width. They rise isolated in the midst of a broad alluvial plain, sloping gradually on the east and west towards the respective valleys of the Sta. Maria and Corralitas rivers. A wide intervening depression also separates them from higher mountain ranges north and south. The latter mountains present a marked contrast in their precipitous sides and exposed rock of a basaltic character to the uniform smooth outline of the mineral-producing mountains. In these latter, indeed, the geological formation is everywhere concealed from view by a variable deposite of earth and gravel, thickly covered with a growth of grass. It is this fact which has probably given to these mines their Spanish appellation of "Minas del mineral de la Escondida," or hidden mines.

The mines at present worked occupy the most northern point of the mountains, though mineral indications and abandoned excavations are common over the exposed face of the whole mountain range. The various excavations bring to view a very uniform character of formation, first passing through a variable layer composed of angular fragments of rock, imbedded in a dry brown earthy medium. The superficial rock exhibits a siliceous limestone of very close compact texture and dark blue color; to this succeeds the true silver-bearing rock, being a form of subcrystalline limestone showing the action of internal heat, of a much softer texture than the preceding, and of a whitish gray color, (specimen rock, No. 99.)

In this latter rock are exposed the veins of argentiferous galena, frequently extending into the upper siliceous rock, but acquiring its greatest thickness and richness in this lower formation.

The veins of mineral penetrate this rock in the form of variable sheets, dipping regularly at an angle of 45° to the northwest.

Further details in reference to the character and working of these mines, with such reliable mining statistics as could be procured, will be found under a separate head.

From the mines, by a gradual and continuous descent over a wide grassy plain, scattered with low mezquite bushes, we have in view at the lowest depression the valley of the San Miguel or Corralitas river, and the towns of Baranca and Corralitas. This plain, though usually dry,

supports a fine growth of nutricious grasses, and the mezquite bushes, which are scattered over its surface, are the main dependence for the necessary supply of charcoal for smelting operations. To first view, this would seem to offer but a poor supply of this needful article, showing in such situations only a shrubby growth; but owing to a remarkable peculiarity of this variable and wide-spread shrub, it is found that, when growing in such exposed situations, instead of developing a distinct trunk, it forms thick underground stems. These being grubbed up by a class of peon laborers, are disposed in piles to dry, when they become fit for conversion into a superior article of charcoal.

At a distance of 20 miles over the above described plain we reach the valley of the San Miguel river; on the eastern bank of which, at a distance of three miles apart, lie the towns of Corralitas and Baranca. We here encounter a beautiful limpid stream and a fertile valley. At Corralitas, this river, as seen by us in the month of February, and again in April, 1852, had an average width of 30 feet, and 2 feet in depth, flowing over a sandy or pebbly bed between shallow alluvial banks. The season of high water is said to be in September, corresponding with the close of the rainy season; at which time a large portion of the adjoining bottom-land is overflowed, the greater part of which is susceptible of cultivation. The width of this alluvial belt is variable, being occasionally spread out in low marshy tracts, 3 to 5 miles wide; at other places contracted by the encroachment of mountains on either side. Some 16 miles above Baranca, to the south, are the remains of ancient and extensive structures, known as Casas Grandes," still occupied by a flourishing agricultural settlement under the same name. A similar character of mountain ranges, as before noticed, bound the valley on either side; being, however, composed exclusively of igneous rock, the higher peaks showing generally a basaltic structure. The towns of Corralitas and Baranca are built up exclusively with a view to mining operations, the ore being transported to these places for smelting and refining. Living in a state of constant warfare with hostile Indians, the raising of cattle, or even the cultivation of the soil, is confined to a bare supply of necessaries. Abandoned fields and deserted ranchos are frequently met with, showing a quite recent period of greater prosperity, the decline of which is most evidently due, not to the natural incapacity of the country, but the inefficiency and degeneracy of its population.

In a direction W.N.W. from Corralitas, and about 24 miles distant, is the town of Janos. Our road to this place, after crossing the Corralitas river, leads at first over the wide grassy bottom-land of its western side, here nearly 5 miles in width. From this we pass over a ridge projecting into the valley below, and descend again on its opposite slope, following near the course of the lower valley, and passing over a shrubby plain similar to that before described, forming a sort of table-land gradually sloping toward the river. The town of Ianos is situated on a branch of this main stream flowing from the southwest. On reaching the banks of this latter stream, we find à mere rippling brook running over a pebbly bed. A short distance below, its waters are drawn off for the purpose of irrigating the gardens and cultivated fields which occupy the delta formed at the point of junction of the Janos branch with the San Miguel river. The town is situated on the gravelly table-land on the left side of the stream overlooking the river bottom, and set off in the background by a range of high mountains shutting out the view westward. Our route leads directly toward this western mountain range, which is crossed at a low depression, thence descending into still another wide basin plain,

extending in its greatest length from north to south, and bounded on the west by the clearly defined range of the Sierra Madre.

The course we travelled thence lies W.N.W., inclining towards this mountain range, and crossing diagonally the wide basin plain intervening between this and the Janos range of mountains. About 10 miles from Janos we come upon a singular depressed valley, sunk some 50 feet below the gravelly plain, having a lower alluvial belt about a quarter of a mile in width, which is coursed by a limpid brook, and bordered by a scattering timber growth.

This stream is said to have a lagoon source some three miles to the southwest; thence flowing northeast 10 or 15 miles, it terminates in a marshy lake surrounded by mountains; thus showing a character similar to that before noticed in reference to Lake Guzman and Sta. Maria on a smaller scale.

From this point, following a continuous course W.N.W. (mag.,) the road passes over a gently undulating swell, composed of gravelly table-land, thence crossing a wide, open, alluvial basin, similar in character to those before described.

We then approach the high mountain range of San Luis. Our progress toward the mountain base leads by a gradual ascent till a near approach brings to view deep gullied stream beds, connected with the drainage of the mountain valleys, and terminating on the alluvial plains below. Near their sources in the mountains these ravines contain running water, more or less copious, according to the character of the season.

On reaching the first rocky spurs from the main range, the country assumes a most picturesque character. Clumps of live oak (Quercus Emoryi) edge the ravines, and are scattered along the mountain slopes. Cedar of a shrubby growth is also frequent, and the usual mountain shrubbery serves to give a character of freshness and verdure to the scenery.

Directly at the mountain base, and forming its projecting spurs, a reddish form of porphyritic basalt makes its appearance, showing a precipitous columned face and tabled summit.

In the recesses of the ravines, as exposed by the mountain torrents, a variable deposite of igneous conglomerate is met with, flanking the central rocky mass. This central nucleus, as exhibited along the sides and summit of the mountain range, is an igneous volcanic product of quite recent origin, and characterized by Professor Hall as "feldspathic lava," exhibiting a granitic appearance. (No. 86.)

At the point where the old road crosses the ridge, called the "San Luis Pass," the ascent is quite abrupt, rising from the plain below 800 to 1,000 feet.

The summit crest commands a most extensive and grand view. Looking eastward, the eye takes in at a glance the wide alluvial plain over which we have been passing, encircled by its irregular mountain boundaries, showing plainly its basin character, and in which here and there stand out isolated mountains, as islands in the broad expanse.*

To the north and south is a continuation of the main ridge, more broken to the north, and apparently forming slopes of easier ascent than the one passed over by us. Quite possibly at several places there may be an easy transition from the plains on one side to those of the opposite slope. To the south the range is more continuous, of a rugged character, and increased height.

This description was written before the line under the treaty of 1853 was run. It will have been seen in the preceding part of this work that good passes were found to the north and within the limits of the United States.

W. H. E.

Westward we look down on another alluvial plain, less distinctly bounded by mountain ranges, and extending to a great distance from north to south. On its western limits, at a distance of about ten miles, this plain abruptly terminates by a slightly elevated terrace, the descent from which to the lower level of the San Bernardino valley forms the well known Pass of Guadaloupe.

Here, then, we have the means of estimating the true character of this great water-shed, in its connexion with the present line of boundary both to the north and south.

Considerable confusion has arisen from the vague terms and expressions employed by writers to describe the peculiarities of this part of the central axis of the North American continent. There has been wanting in their popular descriptions the elements of a general principle, applicable alike to all great dividing ridges. Geological science alone furnishes this element, giving, in the general result of its observations, the best means of elucidating all the points involved, and clearly explaining the several local peculiarities exhibited.

In most of the descriptions hitherto given of this portion of the dividing ridge, we hear in frequent use the stereotype expressions that at or near the point under examination the range of the Rocky mountains becomes "suddenly depressed," or "flattened out," to form the great Mexican plateau. Again, that at some imaginary point south of this great change of topographical features rises another distinct range, called the Sierra Madre, continuing thence to form the line of cordilleras extending to the extreme of the continent.

Now, such descriptions as these embody no clearly defined principle of geological science, and contain, moreover, errors of fact.

The Spanish name of Sierra Madre (literally mother mountains) is the general term in use to describe what is called a dividing ridge with us, and its special application to the range under consideration is due to the important character of this divide as the mother range of the continent. Now, it is well known that all extended continental ranges are due to a line of internal disturbance, of varying intensity at different points, but in all alike characterized by the protrusion of various igneous products, together with the uplifting of adjacent stratified deposites, either altered in texture by the action of internal heat giving rise to the various metamorphic products, or showing the action of an uplifting force only in changes of inclinatian or dip of the strata. Most naturally, then, in view of the numerous and varied agencies at work, should we expect changes of character at different points of the same range, corresponding to points of greater or less intensity of the internal disturbance, or the different products erupted or exposed to alteration. Hence occur elevations and depressions, and variety of formation in the course of the same continued range.

With this principle in view, we have a ready explanation of all the peculiarities exhibited in the portion of the range under examination.

Thus the igneous products are mostly of modern origin, exhibiting various volcanic products in the form of granitic lavas, porphyritic basalts, and amygdaloid traps. These products show a very variable character of exposure, forming ranges irregular in their direction, and differing in composition.

These several mountain ranges cover more or less the entire face of the country, including the dividing ridge only as one member of the general series.