is entirely made up of a coarse quartzy conglomerate and of brown mica. ceous sandstone, which in many places seems to be metamorphosed and becomes jasper-like. No fossils were observed. At the foot of the precipice mentioned above lie large masses of the conglomerate broken off from above and scattered in all directions. Nothing of interest breaks the monotony of the river-bottom and the terraced mesa above, until the Big Horn Mountains are reached, which consist of the same materials as Antelope Peak, but they repose here on a granitic basis. Northeast of these mountains, on the opposite side of the river, occurs a hot spring at the foot of a series of erupted hills, which is much visited by invalids. It is located on Colonel Woolsey's ranch, and is well known throughout Arizona. Fourteen to sixteen miles east of this place the traveler enters on one of the most extensive volcanic overflows met with in Arizona. It is thirty-five miles broad from west to east, and extends for a much greater distance from north to south. The material is a dark basaltic lava, which covers the plateau to the depth of from 2 to 25 feet. The Gila River has cut through this overflow from east to west, and this cañon, as well as several side cañons, across which the road leads, afford a fine opportunity to study the formation. In nearly every place where the lower edge of the lava is exposed, a thin layer of yellowish white soft sandstone is found underlying it. It contains no fossils. This sandstone occupies evidently a vast portion of Southwestern Arizona. I have found it on the plains north of the Salt River, and also north of Florence. It is difficult to determine the source of the enormous mass of eruptive material which covers the plain; for although it is certainly slightly inclined toward the southwest, and several cones are visible at a distance north of the Gila, to which the lava extends, and in the neighborhood of which the hills, too, are capped with thick layers of the erupted material, it is difficult to imagine that these floods could have traveled sixty or seventy-five miles without cooling, and the overflow may have come, at least in part, from the southeast, where in the distance several crater-shaped mountains are also visible. The lava plain is broken in one place by several hills, through a cañon of which the road leads, and where whitish trachytes, containing much olivine in the seams, and red porphyries are exposed to view. On the basalt mesas, the "mal pais" of the Mexicans, the Cereus giganteus, is found in abundance, and in beautiful specimens.

To the east the road leaves now the river and passes across a peninsula formed by the Sierra Estrella and the Gila River for forty-five miles, where it reaches the Maricopa Wells. The Sierra Estrella consists principally of syenites, which are sunburnt and dark on the outside. Looking at the outline of the crest of a part of this range from a cer tain position to the east of it, it shows a striking resemblance to a man's head. This is called Montezuma's Head by the Pima Indians.

Above Maricopa Wells the road strikes the river again at the Pima villages. Here the Gila has formed very extensive bottom-lauds, which stretch away to the cañons, where the Gila breaks through the Pinal Mountains, a distance of about thirty-five miles. At Sacaton the Tucson route leaves the Gila in a southeast direction. The whole distance to that place the road leads over a level country, consisting of gravel and sand mesa, which is only in a few places broken through by syenitic and porphyritic upheavals, viz, between Sacaton and Bluewater, where in the cañon gneiss is exposed besides syenite, and at the Picacho and the point of the mountain, both composed of a reddish trachytic rock. East of Tucson the mesa is traversed by several extensive mountain ranges, the most important of which are the Sierra Catarina, the Sierra

Calitro, and the Pinal Range, the continuation of which toward the south are the Chiricahui Mountains. The Sierra Catarina consists of granite, trachyte, porphyry, basalt, and sandstones on its southern extremity, the latter overlaid by basalt and porphyry. Dr. Antisell thinks these sandstones are Devonian, as they underlie the Carboniferous limestones appearing farther to the east in the Sierra Calitro. In the val thley of the San Pedro gypseous (cretaceous) rocks underlie the whole depression between the Sierra Catarina and the Sierra Calitro according to the same authority, and these are covered toward the south near the head of the San Pedro by Tertiary gravel conglomerate.

The Calitro Mountains are made up principally of a thick red sandstone formation capped almost throughout by Carboniferous limestone, which in turn is in some places covered by trappean rocks. The next range to the east is the Chiricahui Mountains, which consist of granite overlaid on its flanks by the sandstones and limestone mentioned before. Between the two last-named mountains lies the Playa de los Pimas, an extensive plain, under which the sedimentary strata appearing on the flanks of the ranges dip from both sides. To the northwest of the Chiricahui Mountains rises the Piñaleno Range, of which the former is only a southern extension. It is one of the longest ranges in Arizona, reaching northwest as far as the Rio Verde in the vicinity of Camp McDowell. It is composed of the same materials that compose the Chiricahui Mountains, but reaches a much higher elevation.

North of the Gila and Salt Rivers and west of the Verde, the country looks very much like that immediately west of Tucson. It is an immense plain, which rises to the northeast and north until it reaches the Tonto plateau in the first, and the foothills of the Sierra Prieta in the second, direction. The mountains in the vicinity of the Upper Salt River crossing consist of granite, on which rest red sandstone and course conglomerates dipping to the west. The same conglomerates compose the isolated hills to the south of the road from Salt River crossing to Phoenix, while north of that road appear metamorphic slates in the mountains. The plain is here underlain by a thin layer of soft, gray sandstone, probably the same which underlies the basalt overflow mentioned as occurring on the Gila River. In some of the arroyos of this plain a light-colored, soft limestone is visible, underlying the sandstone, very similar to that found at Tucson, which is considered Cretaceous. No fossils were noticed in either of these strata.

On the road from Phoenix to Wickenburg the road leads continually over the mesa without striking any of the "lost mountains" visible on both sides at a distance. The mesa is thickly covered with gravel and detritus from the mountains to the north and northeast, and no rock in place is visible until, about twenty miles south of Wickenburg, the cañon of the Hassyampa is reached. Here are exposed for the whole length of the cañon proper, about fifteen miles, great masses of red and gray sandstone, frequently metamorphosed, and never exhibiting a distinct stratification. In fact, this district has evidently been greatly disturbed, as becomes apparent, on the road from Wickenburg to the Vulture mine, and also on that to La Paz, where the metamorphic slates stand almost vertical.

Directly northwest of Wickenburg, over a level mesa and eighteen miles distant, rise the Martinez or Date Creek Mountains. They are entirely composed of granite and syenite, much crossed by dikes of green stone-slate and quartz. Following the road from Camp Date Creek to Prescott north, an elevated table-land is crossed, which is entirely cov ered with scoriæ. It forms the divide between Martinez Creek and the

head-waters of the Santa Maria. Bell's Cañon, a grand cut through vast granitic accumulations, which. are frequently crossed by quartzite dikes, is passed in descending in the valleys to the north, which are formed by the creeks running into the Santa Maria. These valleys form beautiful basins, and are covered with a fertile soil. The geology of this region is very interesting, but the party being very weak the imme diate vicinity of the trail could not be left on account of the hostile Apache-Mojaves, which swarm in these rocky defiles. The great bulk of the rocks, howevever, is granitic, but metamorphic rocks abound, and in one of the valleys large masses of white sandstone standing isolated in the valley, as left by erosion, were noticed, and opposite, more than one thousand yards distant, the same beds could be observed forming the mar gin of the valley toward the east and disappearing under the gravel covered mesa. Vegetation is here improving continually, as the road approaches nearer to the Sierra Prieta, and the whole surface rises very rapidly. In the valleys live oak, cedar, and a dense chaparral of a small bush-like oak are met with until at the northern base of the Granite Mountain, around which the road leads, the first juniper and pine forests are met with. The western and northern base of the Sierra Prieta, the northwestern terminus of which is Granite Mountain, is flanked by a broad belt of metamorphic slates, which extends west to Williamson's Valley, the slates standing steepest nearest to the main granite ridge. Granite Mountain presents a very imposing spectacle. Rising 3,000 feet above the valley north of it, its rugged sides are cov ered with immense granite boulders, which are piled up in the most picturesque manner. Its greater part is uncovered by vegetation, but on the northern slope the ravines coming down from the central ridge are thickly covered with large pine to the top. Toward the southeast it runs out into the pine and grass covered Sierra Prieta Range. This range contains all the mining districts in the vicinity of Prescott, and, as I shall refer frequently to its geological structure, I will here dismiss it, saying only that it is made up principally of granitic rocks, which are often cut by dikes of porphyry and greenstone, and flanked by metamorphic slates in every direction. It is over sixty miles long and about thirty-five miles wide. To the east and north of it stretch the Tonto and San Francisco plateaus, separated from it by the Val de Chino and the Agua Frio Valley. The Tonto plateau is reported to be underlain by limestone and sandstone, and as it is only part of the great tableland to the east accidentally cut off from it by the deeply eroded valley of the Verde, the latter is probably formed by the same rocks. Still farther to the east lies the great Mogollon Range, the geology of which is not known. It is the home of the most dangerous portion of the Apaches, and has not yet been explored satisfactorily.

In Northern Arizona the sedimentary strata underlying the extensive plains and table-lands stretching almost unbroken from the Colorado River to New Mexico and north into Utah Territory are better exposed to view than in other portions of the country. The Great Cañon of the Colorado has been eroded over 6,000 feet deep, and exposes all the sedi mentary strata of the region down to the underlying granite. Dr. New. berry, in his admirable report on the geology of the ronte explored by Lieutenant Ives's party, in the latter part of 1857 and spring of 1858, says, in relation to this stupendous cañon, and the country to the east and

northeast of it:

"That portion of the central plateau which lies west of the Rocky Mountains varies in elevation from 5,000 to 8,000 feet; the smaller number representing the altitude of its surface where deeply eroded. Its average altitude in the vicinity of our route may be estimated at 6,000 feet.

"Over this plateau the Colorado formerly flowed for at least five hundred miles of its course, but in the lapse of ages its rapid current has cut its bed down through all the sedimentary strata, and several hundred feet into the granite base, on which they rest. "For three hundred miles the cut edges of the table-lands rise abruptly, often perpendicularly, from the water's edge, forming walls from 3,000 to 6,000 feet in height. This is the Great Cañon of the Colorado, the most magnificent gorge, as well as the grandest geological section, of which we have any knowledge.

Section of the Cañon of the Colorado on the high mesa west of the Little Colorado.

[For heights above the Colorado subtract 1,300 feet from the heights above sea-level.]

"That portion of the table-lands lying between the mouth of the Virgen and the Little Colorado is composed of over 4,000 feet of sedimentary rocks, representing the Silurian, Devonian, and Carboniferous epochs.

"The Silurian and Devonian strata are entirely conformable among themselves and with the Carboniferous rocks. They lie nearly horizontally upon the granite, forming a series of sandstones, limestones, and shales about two thousand feet in thickness. The Carboniferous series consists of over two thousand feet of limestones, sandstones, and gypsum, apparently all marine, and often highly fossiliferous. The upper members of the latter series form the surface of the mesas west of the Little Colorado, upon which the volcanic group of the San Francisco Mountains rests as a base.

"North of the Colorado, near the Mormon town of Parawan, it is said that the true Coal-Measures make their appearance, with workable beds of coal; but south of the river an open sea existed during the entire Carboniferous epoch; the 'mountain limestone' appearing, if at all, in the cañon of the Colorado, and the Coal-Measures being represented here, as is the case farther eastward in New Mexico, by massive beds of limestone, heretofore considered, as I think erroneously, the equivalents of the lower Carboniferous or mountain limestone.""

"The strata composing the plateau bordering the Great and Little Colorados by their dip form an elongated basin, of which the greatest diameter extends from the Mogollon Mountains northwesterly into Utah. The Great Colorado crosses that line nearly at right angles; the course of the Little Colorado being parallel to and locally coincident with it. Near the western margin of the basin some of the older sedimentary strata are seen dipping eastward, resting on the flanks of the mountain chains, which I have described as bounding the plateau in that direction. They here present bold escarpments toward the west, oftener the result of erosion than fracture. They have evidently been clevated by the upheaval of the plutonic rocks upon which they rest; but as they are usually quite unchanged, the igneous rocks could not then have been in a state of fusion, but were themselves the products of anterior eruptions. The oldest Paleozoic rocks are nowhere on our route included in the elevated escarpments to which I have referred; and in the Great Cañon the lower members of the series are seen deposited around and abutting against pinnacles and ridges of granite, which seem to be spurs from the Cerbat or Aztec Mountains. Hence it appears that the mountain chains which bound the plateau on the west existed, at least in embryo, before the dawn of the Paleozoic period, and formed a barrier which, to a great degree, limited the deposition of the Silurian and Devonian strata to the basin-like area lying east of them."

"The same phenomena recur on the other side of the plateau, near the Rio Grande, where the Carboniferous strata are upheaved in many places, and are seen to rest directly upon the granite. The absence of the older rock in both instances is doubtless dependent upon a common cause.

As has been mentioned, it may well be suspected that some of the strata composing the great platean recur on the western side of the Black Mountains, beneath the Tertiaries of the synclinal trough of the Colorado basin; and that fused they form some of the porphyries, trachytes, &c., which characterize the mountain chains of that region.

The Silurian and Devonian sandstones are not recognizable in any of the metamorphosed strata of the Peninsular Sierra, (nor are any of the rocks of the table-lands, unless, perhaps, the Carboniferous limestone,) though they may be represented by the foliated granites and schists. It is quite possible, therefore, that the sediments derived from the erosion of the land during the older Paleozoic periods did not extend so far into the ocean, which bordered it on the west.

"In crossing the table-lands in a direction from southwest to northeast, or nearly in the line of the transvere diameter of the trough formed by the strata, I obtained a section, of which the general features are as follows: Leaving the Lower Colorado, where its bed is less than 500 feet above the sea-level, we crossed three mountain chains, of which the eastern bases are, respectively, many hundred feet higher than the western. When we had passed the third of these ranges, at an elevation of nearly 5,000 feet, we found ourselves on Lower Carboniferous strata, of which the upturned and broken edges form part of the crest of the mountains. They thence extend eastward in a plateau, having a distinct dip in that direction.

"This plateau is locally much broken and covered by floods of lava, which have flowed from the mountains we had passed; and yet, from commanding points of view, we could see that it had a distinct existence, stretching far away as a margin to the mountains, in a northwesterly direction. It is bounded on the east by a wall several hundred feet in height-in many places perpendicular, and generally abrupt-formed by the cut edge of a portion of the Middle Carboniferous series. Having ascended this wall, we found our view again limited on the east by the bold escarpments of the edge of another and much higher mesa, which, with its salient angles, stretched away in magnificent perspective both to the north and south.

"The surface of this mesa has an altitude of nearly 7,000 feet, due in part to a line of