Malpais-literally, bad land; the "Mauvais terre" of the French. In Sonora it is exclusively applied to mesas, lomas, or any more or less elevated plateau formed of igneous rock, here mostly a compact or vesicular trap or basalt.

Ciénaga is a valley, or depression in a plain, where the water collects, and can only escape by an obstructed outlet. Such a place is usually miry and boggy.

Charco means a hole in clay, or stratum of rock, where water collects, and from which it cannot run.

Tinaja is a water-hole, found in the crevices of rocks and ravines, difficult of access. The primary meaning of this word is an unglazed earthen jar, burned so as to allow exudation. The water thus oozing through evaporates and keeps that remaining inside cool.

Beginning at the intersection of meridian 111° and parallel 31° 20', we proceed to the consideration of the various sierras crossed by the line.

The Sierra del Pajarito (little bird) shows crystalline transition rocks, metamorphic and unchanged; also, trachytic strata, or metamorphic forms of granitic and syenitic rocks, (E.) Some of the more elevated portions exhibit a rough cellular surface, whilst the lower are smooth and more compact. The tint is light pink, or flesh color. This rock contains much glassy feldspar, and, occasionally, particles of augite, indicating the frequent occurrence of a syenitic granite. A fine-grained, white, metamorphic syenite, consisting of minute particles of hornblende and white feldspar, occur on some of the cuchillas on the north side. On the lower parts of the west slope talcose (argillaceous) and quartzose slates are met with, though trachyte dykes range through in every direction; in the bottom and slopes of the valleys the igneous rocks prevail. In one place a solid mass of trachyte is cut through by an arroyo, forming a puerto, flanked on both sides by vertical walls of eruptive (A and c) rocks fifty feet thick. The mountains on both sides slope towards this gap at an angle of 35 to 40 degrees. Here, and other localities along the foot of this sierra, pudding stone, volcanic breccia, feldspathic porphyry, and trapitic amygdaloid rocks abound. Some of the water-beds are lined with a singular formation, (B,) and apparently of a later age than those just mentioned. At first sight it may be considered a fresh-water deposit, overlying or placed alternately with volcanic breccia.

Occasionally traces of stratification, and even cleavage, are visible, especially in its upper part; its lower portion is cemented into a solid mass. Its color is a light brown, or dark ashgray. The outer crust looks as if it had been subjected to a process of calcination, for it readily crumbles or exposes a marl or chalk-like substance that could be easily scratched out with the finger. There were no means at hand to identify this as carbonate of lime; yet we were

inclined to the belief that the whole mass of apparent fresh-water deposit was cemented by this material, which also formed the matrix of the volcanic breccia. The trapitic and amygdaloid rocks (F) appeared everywhere, no matter how great the elevation, slightly blended with carbonate of lime, as if it had been precipitated there by water. This calcareous precipitation was espe

cially perceptible in the vesicular cavities of every trachytic or basaltic boulder, and also in the fissures of the rocks and in the dells where these latter are imbedded.

On the east slope, in the valley of "Los Nogales,' (Walnuts,) similar strata line the various

VALLEY OF "LOS NOGALES."

water-courses, sometimes forming a continuously winding low bank, or terrace, on both sides, and sometimes covering the slopes of the adjoining mountains, composed of metamorphic rock. On the hill-sides there are beds of this formation dipping towards the valley, and exhibiting, by decurrent, undulating lines, a shaly, laminated texture. On the easternmost limits of this valley the same formation is still more developed; and it can be seen in all the valleys to the south and southeast of the Sierra de Santa Barbara, which is a part of the cordillera embracing the Sierra del Pajarito. The volcanic breccia, in many of the ravines, form walls of from forty to fifty feet in height, varying from an angle of forty-five degrees to perpendicularity. Pieces of this breccia, heated in a log fire, and then thrown into cold water, showed much effervescence, without fracture.

North and northwest of this mountain range, bearing east and west, the Sierra Janos rises up in bold terraces of dark-brown amygdaloid trap and porphyry, the broader terraces being nearer the base. These gigantic shelves are bordered with rocks projecting out in the most fantastic shapes. They incline toward the main body of the sierra-deep and lateral valleys intervening. A huge block, exhibiting on its south and west side gigantic walls, with distinct stratification and cleavage intersecting at right angles, constitute at once the centre mass and the peak. The rectilinear fissures are visible at a distance of ten or fifteen miles, and giving the igneous walls more the appearance of mason-work than the result of volcanic action.

This sierra's vernacular name, "Janos," bears no reference to its petrographic character. The word signifies, in the language of the Papago Indians inhabiting this country, an arborescent shrub of the bignoniaceous order, belonging to the genus "Chilopsis." Its frequent occurrence here in the water-beds in this vicinity may have originated the name.

On the northern slope of the Sierra Janos another group of mountains occur, known as the Sierra Atascosa. Its bearing is the same as that of the Sierra Janos, and its longitudinal axis is common to this sierra and that of Sierra del Pajarito. All these three links of the cordillera have both dip and strike alike, the dip being to the east. Its petrographic character is similar to that of the Sierra Janos, and, being closely connected orographically, may be considered its twin. The cordillera formed by these three mountains terminates with the Sierra Atascosa, which is separated by a narrow and rugged valley from the Sierra del Babuquibari, lying to the northwest. This valley is of some importance, not only for its valuable fresh-water springs, .but also as affording the only means of communication between the settlements of the Santa Cruz River valley and the coast regions along the Gulf of California. A rancho was once established at these springs, bearing the Papago name of Aribaca, or, more properly, Aribac. The settlement has, however, been abandoned long ago, in consequence of the repeated depredations of the Apaches. The northwestern part of the sierra is composed of igneous rocks, towering up into peaks of the most grotesque form, and bearing, not inappropriately, the name of "Malpais."

Atascosa means "miry," which probably has reference to a previous state; it now presents the appearance of being an upheaved, boiling, volcanic pool. This sierra and that of Janos have about the same elevation above the Santa Cruz valley.

Springs abound about the Sierra del Pajarito, but their drainage being, for the most part, below the surface, it requires a well-practised eye to detect their presence, particularly during the dry season, which occurs in April, May, June, and sometimes July. There is a considerable

development of vegetation on this sierra; the rough surface of its sides is covered with a dense growth of shrubbery, of which some are quite trees, and grass is luxuriant in all the valleys. There are several species of oak, and on the summit is found a cedar; though this ridge does not fully reach the pine region. This sierra partakes of all the physiographical features of the Santa Barbara, Santa Cruz, and other links of the Sierra Madre further east. The Sierra del Pajarito, with its dependencies already referred to, constitute one and the same mountain system, properly characterized by the word Cordillera, and, taken collectively, are known as the Arizona Mountains. This word probably belongs to the soft Papago language, but we could not learn its meaning. The Arizona Mountains are rich in silver, copper, and gold; evidences of numerous and well-worked mines are still to be met with. The eastern slope of the Sierra del Pajarito (Los Nogales) is especially worthy of exploration with reference to a development of its mineral production. Specimens of silver from this locality were analyzed, and the result will be found in its proper place.

The Sierra del Pajarito constitutes a part of the divide already referred to, and has been intentionally dwelt upon at length for the purpose of referring the other sierras to it as a standard of comparison in consequence of its typical character, both as to its hypsometrical and geological features.

Looking westward from the peak of the Sierra del Pajarito, a rugged net of mountain ranges is spread out, made up of metamorphic rocks; and though the single sierras do not rise very high, they form a very bold mountain relief by the close, uninterrupted texture of the inclined plane which constitutes them. (See outline sketches Nos. 34 and 35 of the azimuth line.)

At a distance of about sixteen miles another cordillera is visible, between which and the Sierra del Pajarito very little drift occurs; and this is confined only to the intervening valleys, where mesas and lomas, forty to fifty feet in height, are formed by the drainage from the surrounding mountains. Near where the drainage from the east slope of the Sierra de la Escondida joins that coming from the southwest side of the Sierra del Pajarito, a point just south of

D

C

SECTION ON THE NORTH SIDE OF THE CERRO DE SONORA.

the line, permanent water is to be found. It is under a cleft of igneous rocks, and does not properly deserve the name of a spring, but is rather a tinaja supplied by water trickling through the rocks from water-holes above. From the character of this place is taken the name Escondida, (agua escondida meaning hidden water,) a term which is generally applied to the whole sierra. In its orographical character, this sierra is but a volcanic dyke, (A) towering up into an isolated, rugged crest of igneous rocks, composed of amygdaloid, porphyritic, and trachytic compounds, intersected and overlaid by contorted and overthrown crystalline strata of a coarselygrained and frequently disintegrating feldspathic syenite (B.) This syenite is sometimes meta

morphic, at other times unchanged; sometimes it is quartzose, and imperfectly mixed with large scales of silvery mica, in other places feldspar prevails.

This sierra is scarcely more than one mile wide where the line crosses it; both sides are bordered by the upheaved and contorted crystalline beds just alluded to. We ascended to the top of this sierra, near where the singular-looking peak that marks the Escondida towers up, and found it to exceed in barrenness either of the sierras-Pajarito, Janos, or Atascosa. Portions of the terrace-like slopes, and also the plateau, are covered with patches of white or pearl-colored chalcedony, investing the rocks with a scoria-like crust of that silicious fossil. The southern part exhibits a more horizontal arrangement, leading to the supposition of having been formed under water; for here are extensive table-lands, ridges, lomas, and mesas, composed partly of black vesicular or compact trap, and partly of real quaternary banks. The topography of the country seems to indicate here the confluence of numerous mountain streams and torrents coming from every direction. (See sketch No. 40 of azimuth line.)

The line crosses a little to the north of a conspicuous peak (D)—the highest point of the whole range and falling on the Mexican side, we gave it the name of "Cerro de Sonora."

Immediately west of the Sierra de la Escondido a low group of granite hills (c) occur, furnishing several temporary, as well as permanent, water places, apparently well known to the nativesPapagos and Apaches. Some are mere tinajas; others real springs, though liable to become dry before the setting in of the rainy season. While encamped here we experienced a heavy hail and thunder storm; in a few minutes water came rushing down the ravines in a torrent, five feet deep, carrying everything before it, and giving us unmistakable proof how little time it requires to submerge all the valleys around under a most terrible flood of rain-water. This mountain group was called "Granizo,” (hail,) and is so designated in the maps from the circumstance of the surveying parties being overtaken here by one of those hurricanes peculiar to these regions.

A flat valley, nine miles wide, separates the Sierra de la Escondida and the adjoining Granizo group from the Sierra Verde, which is a southern spur or branch of the Sierra del Babuquibari, north of the line. The plateaus bordering the dry water-courses of this valley furnish fine grass, and are sparsely covered with well-developed hackberry and liveoak. The Sierra Verde, so called because of the verdure encountered in the shelter of its rocky valleys, seems to be formed exclusively of feldspathic granite, similar to that already mentioned as occurring on the east slope of the Sierra Escondida. The strike-side faces southwest, and with a width of scarcely more than a mile, this sierra does not present any petrographic novelties. Its longitudinal axis ranges southeast and northwest, and joins the bold walls of igneous rocks belonging to the Sierra Babuquibari. At its southern end mounds of dark, vesicular trap crop out of the diluvial main. Here water finds its way to the surface, forming a spring known as the "Pozo Verde," (Green Well ;) the bunches of rush, which at once conceal and mark the water, in all probability gave rise to the name.

Almost due north of the Sierra Verde lies the picacho of the Sierra del Babuquibari, which is one of the orographical phenomena of the country, its peculiarity being such as to attract especially the attention of the red man. The Papagos consider this huge mountain obelisk their palladium; here they take refuge in times of famine, drought, or war. Babuquibari is said to signify "water on the mountain." The word is certainly formed from babu (water) and ari