MINING 299 



sometimes in veins, but occasionally in very largo masses, both in primitive and tran- 

 sition rocks ; as also sometimes in secondary strata ; but more frequently in the coal- 

 measure strata, as beds of clay-ironstone, or globular iron oxide, and carbonate of 

 iron. In alluvial districts we find ores of clay-ironstone, granular iron ore, bog- 

 ore, swamp ore, and meadow ore. The iron ores which belong to the primitive 

 period have almost always the metallic aspect, with a richness amounting to 75 per 

 cent, of iron, while the ores in the posterior formations become, in general more and 

 more earthy, down to those in alluvial soils, some of which present the appearance of 

 a common stone, and afford not more than 20 per cent, of metal, though its quality ^s 

 often excellent. See IRON. 



7- Mercury occurs principally among secondary strata, in' disseminated masses, 

 along with combustible substances ; though the metal is met with occasionally in 

 primitive countries. See MERCURY. 



8. Cobalt belongs to tho three mineral epochs ; its most abundant deposits are 

 veins in primary rocks ; small veins containing this metal are found, however, in 

 secondary strata. 



9. Antimony occurs in lodes among the older and transition rocks. 



10. 11. Bismuth and Nickel do not often constitute the predominating substance of 

 any mineral deposits ; but they commonly accompany cobalt. 



1 2. Zinc occurs in three several formations, namely : as sulphide or blende, par- 

 ticularly in primary and transition rocks ; as calamine, in secondary strata, usually 

 along with oxide of iron, and sometimes with sulphide of lead. 



The study of the mineral substances, called gangues or vein-stones, which usually 

 accompany the different ores, is indispensable in the investigation and working of 

 mines. These gangues, such as quartz, calcareous spar, fluor spar, heavy spar, &c., 

 and a great number of smaller substances, although of small value in themselves, 

 become of great consequence to the miner, either in pointing out by their presence 

 that of certain useful minerals, or by characterising in their several associations 

 different deposits of ores of which it may be possible to follow the traces, and to dis- 

 criminate tho relations, often of a complicated kind, provided we observe assiduously 

 tho accompanying gangues, 



Among the indications of mineral deposits, some are proximate, and others remote. 

 Tho proximate are an efflorescence, so to speak, of the subjacent metallic masses ; 

 the frequent occurrence of fragments of particular ores, &c. The remote indications 

 consist in the geological character, and in the nature of the rocks. From the examples 

 previously adduced, marks of this kind acquire new importance when, in a district 

 susceptible of including deposits of workable ores, the gangues or vein-stones are met 

 with which usually accompany any particular metal. The general aspect of moun- 

 tains whose flanks present gentle and continuous slopes, the frequency of sterile veins, 

 the presence of metalliferous sands, the neighbourhood of some known locality of 

 an ore ; but when ferruginous or cupreous waters issue from sands or clays, such 

 characters merit in general little attention, because the waters may flow from a great 

 distance. No greater importance can be attached to metalliferous sands and saline 

 springs. 



In speaking of remote indications, we may remark that in several places, and par- 

 ticularly near Clausthal in the Hartz, a certain ore of oxide of iron occurs above 

 the most abundant deposits of the ores of lead and silver; whence it has been 

 named by the Germans the iron-hat. It appears that the iron ore rich in silver, 

 which is worked in America under the name of pacos, has some analogy with this 

 substance ; but iron ore is in general so plentifully diffused on the surface of the 

 soil that its presence can be regarded as only a remote indication relative to other 

 mineral substance?, except in the case of clay-ironstone with coal. Tho gossans of 

 Cornwall, occurring in the iipper portions of lodes, are analogous formations to the 

 eiserne Hut of the German miners. 



Mineral veins are subject to derangements in their course, which are called shifts 

 or faults. Thus, when a transverse vein throws out, or intercepts, a longitudinal one, 

 we must commonly look for the rejected vein on the side of the obtuse angle which 

 the direction of the latter makes with that of the former. When a bed of ore is 

 deranged by a fault, we must observe whether the slip of the strata be upwards or 

 downwards; for, in either circumstance, it is only by pursuing _ the direction of the 

 fault that we can recover the ore ; in the former case by mounting, in the latter by 

 descending beyond the dislocation. 



"When two veins intersect each other, the direction of the offcast is a subject of 

 interest both to the miner and tho geologist. In Saxony it is considered as a general 

 fact that the portion thrown out is always upon the side of the obtuse angle, a cir- 

 cumstance which holds also in Cornwall ; and the more obtuse tho angle, the out- 

 throw is the more considerable. A vein may be thrown out on meeting another vein, 



