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Bed Mountain.—A remarkable occurrence has been described in the lied Mountain district, Ouray County, Colorado. In the midst of the deposits of the San Juan region, which are connected with eruptive rocks, appears a body of Mesozoic strata, carrying, at the contact of a quartzite with the underlying limestone, a deposit of the sulphides of iron, lead, copper, silver, and the products of their decomposition, rich in silver and somewhat auriferous (590z. to llloz. of silver and OoBoz. to 0-17oz. of gold per ton of 2,0001b.). At certain points the ores extend far down into the limestone, and in the section shown in Fig. 74 the ore follows a fault-fissure through the whole thickness of the limestone into a second quartzite stratum below. The stratified formation is mostly covered with andesite, in which occur ore-bearing veins in fissure form. In the neighbourhood, at Mineral Farm, another contact-deposit between limestone and quartzite is known, consisting of barite with argentiferous galena and tetrahedrite. Both the above deposits are but briefly described, and perhaps have not been extensively worked. Their conditions of position and the predominance of lead- and silver-ores strangely remind one of Leadville. In the adjacent territories of New Mexico and Arizona various copper-deposits occur in limestone, and at its contact with eruptive rocks, as, for instance (according to the outline-description of A. F. Wendt), in the Clifton and Bisbee districts. The sections accompanying Mr Wendt's paper remind me of some of the deposits described in my monograph at Bezbanya, at Mednorudjansk, and at Bogoslavsk, in the Ural. Fig. 75 is an interesting section from the Clifton district, in Arizona, showing two steep ore-shoots, parallel with the felsite dyke, and a fiat one, parallel with the bedding. Utah. —With respect to Utah, the paper of O. J. Hollister gives a general survey of the deposits of the Territory, and mentions a number which occur in limestone. Some of those in central Utah an opportunity was afforded me to see personally, during the period when mining was still confined chiefly to the decomposed upper levels. Palaeozoic strata are here traversed by frequent eruptive dykes, and by two intersecting systems of faults. The ore-deposits, of varying thickness, in the limestone have, as a rule, the form of " chimneys," either lying flat with the bedding or standing steeply along the dykes and faults. This gave rise in the beginning (when the nature of the deposits was not understood, and the conception of a typical " lode " generally prevailed) to a series of disappointments and mistakes in mining, of which the history of the Emma Mine furnishes an interesting example. Apparently the irregularity and the complications of these deposits came to be better known afterwards. The (sometimes very rich) ores consist chiefly of sulphides of lead and silver, and the products of their decomposition. In some cases (e.g., Hidden Treasure) cuprite occurs, with native copper; and in the Camp Floyd district cinnabar also is found. Nevada.- —ln Nevada, adjoining Utah on the west, deposits of this class are likewise abundantly represented. The two districts which have been most thoroughly studied are White Pine and Eureka. With regard to the former, the work of Arnold Hague (1870), demonstrating the peculiar character of the White Pine deposits, led me to seek for European analogues. It was found that, apart from the condition of the ores, which at White Pine are found in the oxidized and chloridized zone, there was an analogy with all the European ore-deposits in limestone, but especially with the conditions at Eaibl. Devonian limestones and calcareous slates are overlain at White Pine by Carboniferous clayslates, sandstones, and limestones; and the ores occur only in Devonian limestone and at its contact with the calcareous slates on a north and south anticlinal. The ores and the associated minerals (quartz, calcite, gypsum, fluorspar, barite, rhodonite, rhodochrosite, with the chlorides, bromides, oxides, and carbonates of various metals, especially silver, lead, and copper) fill the cavities in the limestone and surround its fragments. The various mines represent different stages in one and the same process. In the Eberhardt, two fissures crossing the anticlinal bound the ore-body (like the Morgenblatt and the Abendblatt at Eaibl). This consists of a lime-breccia (Kalktyphon), the fragments of which fit together, and are cemented by ore-bearing quartz seams. The Hidden Treasure Mine contained the ore in geodes, at the contact of the limestone and slate. In the Aurora, the ore was in bodies stretching north and south. In Bromide, Chloride, and Pogonip Flats, the ores occurred in geodes and masses included in lime-breccia, in a zone parallel with the bedding. It is Arnold Hague's opinion that the Eberhardt Mine probably represents the source of the ore-solutions which impregnated the limestone, wherever cavities existed, up to the level of the overlying calcareous slates, which were impermeable to the solutions. The slate cover having been removed by erosion, the ores thus accumulated below it were exposed immediately at the surface; and the surprisingly large product of the district was derived from open cuts and shallow workings. The other leading analogue in Nevada is found in the Eureka district, and was made widely known and practically significant by the law-suit between the Eureka and Eichmond Companies, which involved the definition of a deposit not contemplated in the United States mining law. Similar difficulties have arisen under the old European mining codes. Such deposits were known in some districts of Europe, but they were not so widely distributed as the fissure-veins, for the conditions of which the ancient codes were framed. Conflicts were therefore inevitable. In Bleiberg in Carinthia (which presents some degree of analogy with Eureka), besides the general mining code, special statutes became necessary, departing from the usual rules with regard to prospecting and the location and the acquisition of claims. According to Arnold Hague, the series here occurring of Prospect Mount quartzite, Prospect Mount limestone, Secret Canon shale, and Hamburg limestone, is Cambrian. The ore is confined to the limestone first named, and in particular to a portion thereof on the north-east slope of Euby Hill, enclosed between two fault-fissures. The features of the N.W. to S.E. ore-bearing zone are too variable to be indicated by a normal cross-section. Fig. 76 shows a generalised and Fig. 77 an actual section as represented by Curtis.