area above, or depress it below, the adjacent country, or not to change its relative altitude. These features are exhibited on a small scale within a limited area, usually so elongated as to be termed a zone. During the past season Mr. G. K. Gilbert has studied an area where this diverse displacement is by faulting, and the faults are of no great inagnitude, and the blocks into which the area has been severed are either not tilted or but slightly so. This presents the simplest illustration of this type that has yet been discovered. It is simply the Kaibab structure on a very small scale. Fig. 4 is a bird's eye view of the blocks mentioned. In FIG. 6.-Types of Displacement. A.-Simple Anticlinal displacement. B.-Uinta displacement. C.-Kaibab displacement. D.-Basin Range displacement. E.-Zone of Diverse displacement. the section, in the foreground, the heavy line represents the summit of the highest Cretaceous group. Fig. 5 is a diagram of the same region showing the blocks into which it is severed, and the same restored to the condition they would have, had there been no denudation. On the south side of the Uinta Mountains, and east of the Green River, another comparatively simple area has been studied by myself. This zone of diverse displacement is on the flank of the great Uinta upheaval. These displacements are chiefly by flexures rather than by faults, and the blocks are more tilted and contorted than in the last. In Atlas, plate No. 4, we have a stereogram representing these displacements, and in a subsequent chapter the subject is more fully discussed. Many other areas far more complex than these have been discovered, where a zone has been broken into blocks, and these blocks tipped and contorted in diverse ways and directions, like the blocks of ice crowded in an eddy of a northern river at the time of its spring flood. The topographic features found in such areas are zones of irregular hills. Figure 6 is a diagram illustrating the general types of displacement heretofore discussed. A represents a Simple Anticlinal displacement; B, a Uinta displacement; C, a Kaibab displacement; D, a Basin Range displacement; and E, a Zone of Diverse displacement. MOUNTAINS COMPOSED IN WHOLE OR IN PART OF EXTRAVASATED MATERIAL. We are not able in the present state of our knowledge to draw legitimate conclusions concerning the relation of the eruptive rocks, so widely distributed through all three of these geological provinces, but the following types of structure have been observed. VII.-Table Mountain Structure. We often find beds of sedimentary strata preserved from erosion by a capping of lava. Such are usually called table mountains; the underlying strata may be horizontal or inclined. Earlier stages of this structure are seen in mesas or low tables, and sometimes in valleys or gulches which have been filled with extravasated material, and erosion has proceeded to a limited extent on either side of these harder masses, carrying away the softer sedimentary material, and leaving the harder volcanic rocks in the midst of the valley; and this may have an elevation less or greater than that of the adjacent country beyond the rim of the valley. A fine example of a table mountain is found in Pilot Butte, in Wyoming Territory. VIII-Uinkaret Structure. Simple sheets of lava may be poured into a valley or on a plain, and serve as a protection to the sedimentary beds which are immediately underlying them, and as the erosion of the adjacent country not thus protected progresses, new vents may be formed along the edges of such sheets and at a lower level. Still erosion progresses, and still new floods of lava are poured out, and still at lower levels, until a mountain is left behind with its central mass composed of sedimentary material, but covered on the summit and flanks with irregular and overlap ping patches of lava. Thus lava bed is imbricated on lava bed, but unlike the tiles of a roof, the upper edge of the lower sheet is placed on the lower edge of the upper. This structure is well represented in the Uinkaret Mountains in Northern Arizona, and has been more fully discussed by me elsewhere. (Vide The Exploration of the Colorado River, &c., page 199 et seq.) IX.-Tu-Shar Structure. When a plain or valley which receives extravasated material from below remains at a base level of erosion during the period of successive eruptions, flood of lava is piled on flood of lava until a vast mass of material is accumulated from which the rains and streams carve mountains. The several beds of which such a mountain mass is composed are exceedingly irregular, from three causes: first, each bed as poured out was an irreg ular mass, due to its degree of fluidity and the character of the ground on which it was poured; second, each bed was more or less modified by erosion, which occurred after it was poured out, and before it was covered by a subsequent flood; and, third, the general mass has been eroded to a greater or less extent in producing the present forms. The volcanic activity being in a region where movements of displacement are in progress, it is often the case that the structure of this class of mountains is greatly modified by such displacements. Mountains composed of such irregular beds of lava are of frequent occurrence in the region under discussion. A fine example is seen in the vicinity of the town of Beaver, Utah Territory, in what are known as the Tu-shar Mountains. X.- Volcanic Structure. When many eruptions come successively from the same vent, and each is a comparatively small amount, cones are built. Cones of such simple structure are of frequent occurrence in the region under discussion. Great complex cones such as are found in other parts of the world do not occur, but a few double and one triple cone have been observed. The great majority of the cones observed are built of cinders on broad sheets of lava, and are in fact concomitant forms of lava mesas. Such cones are comparatively ephemeral, as the scoria and ashes of which they are composed yield readily to atmospheric degradation. Where such a cone exists, still having a well defined crater, its condition testifies to the lateness of its origin, and all the facts relating to the sheet of lava on which it rests fully corroborate the conclusion. From such evidence we are able to infer the recency of much of the volcanic activity in the three provinces. If the human history of America could be carried back to as early a date as it has been in Asia, it cannot be doubted that the earlier chapters of that history would be replete with the accounts of volcanic fires. XI.-Henry Mountain Structure. Sometimes we find the sedimentary strata displaced by a quaquaversal upheaval and the same fractured, and through these fractures floods of lava have poured, and these may lie in patches about the flanks of the mountains, or stand in dikes where the walls of the crevice have been swept away by denudation. In the Henry Mountains we have a fine illustration of this type of structure. These mountains have been studied by Mr. Gilbert during the past season, and in his preliminary report he says: "The eruptions of the Henry Mountains are of a character entirely novel to me, and they were studied with an interest stimulated by surprise. A description of a single one, though it will not stand for all, will serve to illustrate the type. Mount Ellsworth is round, and its base is six or eight miles broad. The strata of the plain about it are horizontal on every side. Near the mountain the level strata become slightly inclined, rising from all sides toward the mountain. At its base the dip steadily increases until on the steep flanks it reaches a maximum of forty-five degrees. Then it begins to diminish, and the strata arch over the crest in a complete dome. But the top of the dome has cracked open, and tapering fissures have run out to the flanks, and they have been filled with molten rock, which has congealed and formed dikes. Moreover, the curving strata of sandstone and shale have in places cleaved apart and admitted sheets of lava between them. So the mountain is a dome or bubble of sedimentary rocks with an eruptive core, with a system of radial dikes, and with a system of dikes interleaved with the strata. It is a mountain of uplifted strata, distended and permeated by eruptive rock." * * * In the foregoing characterization of certain types of structure found in these regions, I have not attempted to adopt a system of exact classification, which should be both inclusive and exclusive as the types do not admit of such classification. No "hard and fast lines" can be drawn. I have simply attempted to indicate the important types with their primary and concomitant forms. It is manifest that the structure of a sedimentary mountain will depend primarily upon two elements-the type of the displacement and the character and extent of erosion. The erosion may be antecedent or superimposed, or it may be consequent, or these methods may be combined, and the erosion may be modified by dip, texture, and other characteristics of the beds producing concomitant forms. For convenience, I subjoin the following synopsis of the types of mountain structure recognized in the foregoing dis cussion. I. MOUNTAINS COMPOSED OF SEDIMENTARY STRATA, ALTERED OR UNALTERED. I.-Appalachian Structure. (Not found in the three provinces.) II.-Simple Anticlinal Structure. Primary topographic form: Plateau with rounded vertical outline. Concomitant forms: 1. Monoclinal Ridges on the Flanks. Ridges only. 3. Inclined Plateaus. III.-Uinta Structure. 2. Monoclinal Primary topographic form: Plateau with rounded summit and abrupt shoulders on the flank. Concomitant forms: 1. Subsidiary Plateaus. 2. Projecting Ridges. 3. Axial Peaks. 4. Flanking Peaks. 5. Interrupted Monoclinal Ridges. IV.-Kaibab Structure. Primary topographic form: Plateau with angular outlines. 2. Slopes of Displacement. 3. Interrupted Monoclinal Ridges on the Flanks. 4. Monoclinal Ridges with Plateau carried away. 5. Projecting Ridges. 6. Cliffs of Erosion. 7. Buttes. 8. Cameo Mountains. V.-Basin Range Structure. Primary topographic form: Monoclinal ridges of displacement. VI.-Zones of Diverse Displacement. Topographic form: Irregular hills. II. MOUNTAINS COMPOSED IN WHOLE OR IN PART OF EXTRAVASATED MATERIAL VII.-Table Mountain Structure. VIII.-Uinkaret Structure. XI.-Henry Mountain Structure. ART. XLVI.-On the Ethers of Uric Acid. Contributions from the Chemical Laboratory of Harvard College; by H. B. HILL,* Assistant Professor of Chemistry. ALTHOUGH the constitution of many of the derivatives of uric acid may be said to be fairly established, the structure of uric acid itself is still a matter of conjecture. The formulæ given by Bäver, Kolbe, Strecker, § Erlenmeyer, Mulder.T Hüfner,** Gibbs,++ Medicus,++ Drechsel,§§ and Mallet; dif* In great part from the yet unpublished Proceedings of the Am. Acad., p. 26. Ann. Chem. u. Pharm., cxxvii, 235. Journ. für prakt. Chem. II, i, 134. Berichte Deutsch. Chem. Gesellsch., iii, 183. Zeitschr. für Chem., 1868, 363. Zeitschr. für Chem, 1869, 176. München. Acad. Ber., ii, 276. Bericht. der Deutsch. Chem. Gesellsch., vi, 1237. **Journ. für prakt. Chem., II, iii, 23. †† Am. Journ., II, xlvi, 289. Ann. Chem. u. Pharm., clxxv, 243. Journ. für prakt. Chem., II, xi, 352. |