C.—B

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stratification, had suddenly turned upward, and it was clear to me that the occurrence represented a peculiar form of fault—namely, a bending of the strata—followed by fracture in the direction of the dislocating force when the limit of cohesion had been passed. Here and there in these steep places the stopes had been carried beyond the contact, and the resulting appearance was as if the steep deposit had been the primary one and had supplied the ore to the contact. Occasionally eruptive breccias were observed along the steep deposits. At lower levels, in the downward continuation of the fissure of the steep deposit, eruptive rocks and thin breccias occurred; and these became predominant in the lowest part of the mine. The structure of the ore-beds was mainly massive, and not crustified. In some places, however, druses had been developed, which showed the same paragenetic succession as the mass of the bed, and which contained pseudomorphs of pyrite and galena after calcite. The thickness of the ore-bed was extremely variable, the greater part of the contact-area being scarcely worth working, while at single points colossal masses of ore were found. These circumstances led me to consider the deposits, not as contemporaneous in origin with the rock, but as subsequently formed by the circulation of mineral waters along the contact-planes. Mining was then active chiefly on the north slope of the Benyes Divide; and the sedimentary rocks were cut off towards the south by andesite. It was pointed out by me that on the south, slope, beyond the andesite, there were various ancient mines that could be explored in depth by means of an adit. This led to the discovery of several deposits, which gave new life to the industry. After cutting through the andesite the explorers found steep deposits at the contact of andesite and limestone, and, in the limestone, near its contact with the mica-slate, a flat deposit which, being above the ground-water level, had been transformed into carbonate of lead. The somewhat complicated conditions are shown in Kg. 70, as far as this can be done in a single section. The deposit at the contact of andesite and limestone indicates at once a genetic connection with the eruptive rock, and renders it probable that the ore-beds also are due to the after-effects of the eruption. Even on the north slope there were some reasons for this conclusion. For instance, at the ore-bodies locally called thonstrassen, ores occurred in the midst of eruptive breccia, which could not be taken for fragments of the original bed. Baron Constantine yon Beust found traces of " ring-ores," indicating a formation in open cavities. Seeking an explanation of all the facts led me to give up the view of J. Grimm, which he, however, still maintained, citing Offenbanya as another instance in which a pre-existing deposit on the contact between limestone and mica-slate had been shattered by an andesite eruption. But in that instance also an opportunity was afforded me to satisfy myself that the then accessible mineworkings showed no fragments of an earlier ore-deposit, but only ore-formations under the influence of the andesite. Grimm had had in mind the deposits of Eodna and Offenbanya when he established, under the first division in his systematic classification, the second subdivision, " Occurrences of Ores as Fragments of Earlier Deposits in Breccias," &c. Offenbanya. —Offeiibiiuya, in the Transylvania gold district, has various deposits analogous to those of Eodna, and also veins, with telluride ores. We are here interested in its mass-deposits, at the contact of limestone and andesite, one of which is illustrated in Fig. 71. Beneath the limestone widely extending through the district mining has disclosed a mica-slate (the so-called underground slate), and at the contact of the two a flat pyritous deposit. The whole stratified series is traversed by andesite ; but near its contact with the limestone a steep, rich massdeposit extends from the surface down to the mica-slate. This deposit is highly crustified, and was evidently formed-in a pre-existing space. The fiat deposit shows no crustification, and may have been formed by metasomatic replacement of the lime at the contact between the impermeable and the soluble rock. The analogy with the conditions on the south slope of the Benyes Mine, at Eodna, is evident, though it is not certain whether, at Eodna, the flat deposit has been followed as yet to its junction with the steep one. Bezbdnya. —Bezbanya in South-east Hungary represents different conditions. Here, in an indistinctly stratified Mesozoic limestone, occur long spaces filled with ore, descending steeply and irregularly in shape like that of the cavity produced by pouring a stream of warm water upon a snow-bank. This extreme case is of great theoretical interest, although such ore-bodies, having but one considerable dimension, and that in the most unfavourable direction for mining, mainlydownward, are not attractive from a commercial standpoint. In the Eezbanya region, lying above clay slates and Permian and Liassic sandstones, appear numerous isolated bodies of limestone, indicated by their fossils to be of various ages, from the Lias to the Neocomian, seldom distinctly stratified, and, when they are traversed by eruptive rocks, often showing a crystalline structure. The ore-filling is mostly confined to the neighbourhood of the eruptives, and sometimes to the contact, where garnet-rock occurs as a well-known product of local metamorphosis. Since my examination there may have been in this region many interesting and scientifically important developments which are unfortunately unknown to me. It will therefore be necessary to confine myself to the description of a single district, cut off from commercial communication, that of Valle Sacca. The name is that of the valley which heads in a high mountain range of Permian and Liassic sandstones, and, after a short course, ends in a wild limestone canon leading into the Galbina Valley. The sides of Valle Sacca consist chiefly of limestone, which is traversed by a number of eruptive dykes and one larger mass of syenitic character. Fig. 64 gives a somewhat generalised section of the north-west slope of the valley and district on the line of the so-called fourth adit. At the adit-mouth is cut the syenite mass, which extends also to the opposite slope; and the adjoining portion of the limestone has been metamorphosed to a crystalline mass, while the limestone further south-west is for the most part still compact. On the west side the limestone adjoins sandstone along aN. to S. line, which doubtless represents a large fault. Approximately parallel to it run the greenstone dykes, which,