128 BOOK V. 



avoid wearing away their clothes and injuring their left shoulders they 

 usually bind on themselves small wooden cradles. For this reason, this 

 particular class of miners, in order to use their iron tools, are obliged to bend 

 their necks to the left, not infrequently having them twisted. Now these 

 veins also sometimes divide, and where these parts re-unite, ore of a richer and 

 a better quality is generally found ; the same thing occurs where the stringers, 

 of which they are not altogether devoid, join with them, or cut them cross- 

 wise, or divide them obliquely. To prevent a mountain or hill, which has in 

 this way been undermined, from subsiding by its weight, either some natural 

 pillars and arches are left, on which the pressure rests as on a foundation, or 

 timbering is done for support. Moreover, the materials which are dug out 

 and which are devoid of metal are removed in bowls, and are thrown back, 

 thus once more filUng the caverns. 



Next, as to ventB cumulate. These are dug by a somewhat different 

 method, for when one of these shows some metal at the top of the ground, 

 first of all one shaft is sunk ; then, if it is worth while, around this one many 

 shafts are sunk and tunnels are driven into the mountain. If a torrent or 

 spring has torn fragments of metal from such a vein, a tunnel is first driven 

 into the mountain or hill for the purpose of searching for the ore ; then 

 when it is found, a vertical shaft is sunk in it. Since the whole mountain, or 

 more especially the whole hill, is undermined, seeing that the whole of it is 

 composed of ore, it is necessary to leave the natural pillars and arches, or the 

 place is timbered. But sometimes when a vein is very hard it is broken by 

 fire, whereby it happens that the soft pillars break up, or the timbers are 

 burnt away, and the mountain by its great weight sinks into itself, and then 

 the shaft buildings are swallowed up in the great subsidence. Therefore, 

 about a vena cumulata it is advisable to sink some shafts which are not sub- 

 ject to this kind of ruin, through which the materials that are excavated may 

 be carried out, not only while the pillars and underpinnings still remain whole 

 and solid, but also after the supports have been destroyed by fire and have 

 fallen. Since ore which has thus fallen must necessarily be broken by fire, 

 new shafts through which the smoke can escape must be sunk in the abyss. 

 At those places where stringers intersect, richer ore is generally obtained 

 from the mine ; these stringers, in the case of tin mines, sometimes have in 

 them black stones the size of a walnut. If such a vein is found in a plain, 

 as not infrequently happens in the case of iron, many shafts are sunk, because 

 they cannot be sunk very deep. The work is carried on by this method 

 because the miners cannot drive a tunnel into a level plain of this kind. 



There remain the stringers in which gold alone is sometimes found, 

 in the vicinity of rivers and streams, or in swamps. If upon the soil being 

 removed, many of these are found, composed of earth somewhat baked and 

 burnt, as may sometimes be seen in clay pits, there is some hope that gold 

 may be obtained from them, especially if several join together. But the 

 very point of junction must be pierced, and the length and width searched 

 for ore, and in these places very deep shafts cannot be sunk. 



I have completed one part of this book, and now come to the other, in 

 which I will deal with the art of surveying. Miners measure the solid 



