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separated, and it must be assumed that a metallic sulphide has here been deposited from an ascending spring. Kg. 10 represents the exposure as sketched in my note-book. Later developments exhibit these relations stiH more clearly. Le Conte and Becker found a shaft 164ft. from the basalt, about 310ft. deep in sandstone, from which drifts had been run northwards at different levels under the outcrops of the deposit. It is to be regretted that their reports are not accompanied with precise descriptions of the mine-workings. In the third level (210ft. below the surface) the drift was 232ft. long, "cutting through the ore-body, and reaching only barren rock on the other side. The fourth level has been pushed 136ft., and has reached the orebody." From these data it is hardly possible to form an idea of the position of the ore-body traversed. The data given concerning the interior structure of the deposits are, however, important. Sandstones and slates are here broken up by fissures in such a way as often to form a breccia. Whether the fragments belong together, and whether they present the relation which may be denominated typhonic, is not stated; but it may be inferred, from the sketch of an ore-specimen from this place, that the fragments do not belong together, and that their condition has been brought about by more extreme dislocations. The subject is highly important for us ; and it is attempted in Fig. 11, although the original is not before me, to represent it according to Le Conte's sketch, so as to place it side by side with the other phenomena thoroughly familiar to me. The fragments of slate and sandstone have somewhat rounded edges, and leave varied interspaces, which are filled partly with a still soft or already indurated paste, containing finely disseminated metallic sulphides, partly with cinnabar, for the most part in coherent crusts. A part of the space is usually empty, exhibiting what may be called a central druse. Sometimes, it is said, the rock-fragments are cemented together with massive cinnabar, and kernels of rock crusted with cinnabar occur frequently. Hot mineral water and gases carrying H 2 S force their way through the interstices of the deposit, as was the case observed in the upper zones. The silica deposits are found in all stages of consolidation, from a gelatinous mass to chalcedony, and alternate with layers (crusts) of metallic sulphides (cinnabar and pyrites). Becker examined the whole neighbourhood, and extended his studies to similar ore-deposits of the region. He does not consider the basalt of Sulphur Bank, as do G. Eolland and Le Conte, to be a lava-stream, but takes it to be an eruptive rock, originating on the spot, which has overflowed a fresh-water formation of recent age. The bottom proper is a cretaceous sandstone. The ore-bearing character extends from the basalt, 52ft. thick, through the fresh-water layers in to the cretaceous sandstone. Concerning its relations in the middle layer we have no data, which is unfortunate, since the effects of the acid waters upon this calcareous material must have been considerable, and it is not unlikely that the deposit had in this region a totally different character. Fresh-water formations adjoining the deposit have preserved to a remarkable degree plant-roots, &c, transformed into lime carbonate; and it would be very instructive to study their forms as metamorphosed by the mineral water. Concerning the chemical constitution of the warm (176° Fahr.) water, according to Becker's analysis it is extraordinarily rich in chlorides, borax, and sodium carbonate. The gas liberated from it often proved to be ammoniacal, and consisted in 1,000 parts of 893 parts CO 2 , 2 parts H 2 S, 79 parts CH 4 (marsh-gas), and 25 parts nitrogen. As to the presence of other metals besides mercury, it is worthy of mention that Dr. Melville found small amounts of gold and copper in the marcasite accompanying the cinnabar, and that G. Becker found in the efflorescence from the mine-workings, besides the substances detected in the mineral water, traces of cobalt and nickel. As will be seen, this deposit furnishes genetic data, concerning not only the ores of quicksilver, but also those of other metals. An ascending mineral spring here passes from the deep into the shallow region, and suffers, besides the reduction of pressure and temperature, the oxidation of its H 2 S, from which result a strong acid and the deposition of sulphur nearest the surface. In depth no sulphur is found, but sulphides of quicksilver and iron, upon or within deposits of silica, both being in distinct alternating mineral crusts. Ic cannot be doubted that cinnabar and pyrites on the one hand, and silica on the other, have been precipitated from the solution which still ascends in these channels. At most, it may be doubted whether this precipitation is still going on. Le Conte adduces in support of the probable continuance of the process the occurrence of silica sometimes gelatinous and soft, as if recently precipitated. Becker and Melville tried to obtain direct evidence of the presence of quicksilver dissolved in the ascending mineral water of today, but their careful investigations failed to find it. Although the water contains ingredients in which quicksilver is soluble, there is no quicksilver dissolved, and it must have been already precipitated by some agent, as, they suggest, ammonia. There are among geologists unbelieving Thomases enough, who will believe in the presence of quicksilver in the mineral solution only when it has been actually precipitated for them ; but there are those, on the other hand, who are convinced by the evidence thus far gathered that the sulphide deposits of this locality proceeded from the ascending thermal spring, whether the process of precipitation is still going on or not. Equally weighty data are furnished by Steamboat Springs in Nevada, to which Laur and J. A. Phillips first called attention, and which Le Conte and Becker investigated thoroughly. In a valley surrounded with eruptive rocks, but underlain chiefly by Archaean rocks, thermal springs may be seen at several points emerging from north-and-south fissures. The action of these springs has covered the ground with a sinter-deposit, predominately of lime carbonates, about 49ft. thick. In this sinter may be traced many fissures, here and there still open, but mostly closed by the deposit of silica on their walls. According to a sketch given by Le Conte, these very clearly crustified deposits extend somewhat above the general level of the surface, forming single mounds or chains of mounds. From some of them hot vapours and gases still issue, chiefly CO 3 containing H 2 S. In others, such emanations have been so greatly diminished that only by listening can the liberation of vapour