MINING 301 



In Cornwall and Devonshire, where different conditions prevail, other terms are 

 employed. 



The lode, or mineral vein, is, as in the former instances, a great line of dislocation, 

 accompanied by minor lines of fracture. Of these Sir H. De la Beche says, ' It could 

 scarcely be supposed that the great lines of fracture would be unaccompanied by 

 smaller dislocations, running from them in various directions according to modifying 

 resistances, which would depend upon the kinds of rock traversed by the great frac- 

 tures, the direction in which they are carried through them as regards the bearing of 

 their strata should they be stratified, and other obvious causes.' The great fractures 

 would often also tend to split in various directions, and reunite into main lines, as in 

 the annexed sketch (fig. 1448), in which a b represents the line of principal fracture, 



1448 



splitting at b b from local causes, and uniting, both towards a and b, minor cracks 

 running into the adjoining rocks at c, c, c, c. These are known as side-lodes, strings, 

 feeders, and branches. 



These strings are sometimes very curiously developed, and illustrate the peculiar 

 force of crystalline action, and all the phenomena of heaves 

 and faults. The following figure (1449) furnishes a good 

 illustration. 



It represents a specimen of strings of oxide of tin in slate 

 from St. Agnes, Cornwall, h h illustrating the heaves alluded 

 to. Sir Henry de la Beche is disposed to refer these to 

 the fact of oxide of tin recementiug fractured masses of 

 slate. We think we have sufficient evidence for referring 

 the action to the crystallogenic force enlarging a fissure, or 

 small crack, producing those lateral cracks, which again, by the operation of the same 

 force, dislocate or heave the original fissure. 



In those lodes we find peculiar mechanical arrangements, which are known by 

 various names ; a lode is said to be comby when we have the crystals of quartz or 

 other mineral dovetailing, as it were, with the metalliferous masses. Bunches are 

 isolated masses of ore found in the lode surrounded by earthy minerals. The 

 upper part of a lode is known as its back, and the accumulations of ferruginous 

 matter which very commonly occur in the backs and near the surface are known as 

 gossans. These are to the experienced miner important guides as indicating the 

 characters of the lode at a greater depth. The country signifies, with the Cornish 

 miner, the rock through which the mineral vein runs, and accordingly as he is pleased 

 with the indications he speaks of its being kindly or the contrary. The softer rocks, 

 whether of clay-slate or granite, are spoken of as plumb, and a plumb granite, or elvan, 

 is greatly preferred to the harder varieties, and spoken of as being more kindly. 



The rock forming the sides of a lode are known as its walls or cheeks. The latter 

 term we have heard of late years in Cornwall, but we believe it to be imported by 

 miners who have worked in the north of England. As all mineral veins incline 

 more or less, the sides are spoken of as the upper and under walls, the upper being 

 usually termed the hanging wall, and the lower the foot-wall. 



The following woodcuts, figs. 1450, 1451, will serve to assist the reader in 

 understanding the peculiarities of mining operations in our metalliferous mines. In 

 fig. 1451, which is a section of one of the lead mines of Cardiganshire, the shafts, 

 which have been sunk on the lode are shown, at varied angles from the vertical 

 and the several horizontal levels. In this instance these levels or galleries have been 

 worked at irregular distances. In Cornwall they are usually ten fathoms apart. 

 The smaller shafts connecting the levels one with the other are called winzes.^ They 

 serve for exploring the lode, or for purposes of ventilation, when the excavations are 

 going forward. When these smaller connected shafts are worked upwards, as they 

 sometimes are, they are called ' risings,' and the miner is said to be working on the 

 ' rise.' In this woodcut the lightest shading is to indicate a portion of this particular 

 mine which was worked out by the Komans. The darker shaded masses indicate portions 

 of the lode which have been very productive of metalliferous matter, and which have 

 consequently been removed. The term counter or caunter lode is given to such lodes 

 as dip at a considerable angle with the direction of the other lodes in its vicinity. 

 Such a lode is shown, fg. 1450, which is, however, inserted principally to explain that 

 where the ' underlie ' of the lode is great, a vertical shaft is sunk at some distance 

 from it on the surface, so as to ' cut' (intersect) the lode at some depth, in this instance 



