MINERAL VEINS AND ORE-DEPOSITS. 771 



intersected by them, while the next below or above has none. But, 

 also, they may descend through many strata to great and unexplorable 

 depths. 



They may cross the planes of bedding at all angles, and in several 

 directions. But, in general, those in a region that were made to- 

 gether are (1) nearly parallel, but occasionally cross, often at right 

 angles ; and (2) are generally similar in material. 



Veins may cut transversely to the bedding, or be parallel with it. 

 In schistose or slaty rocks, if the beds stand at a high angle of dip, 

 the veins often follow for long distances the course of the bedding, be- 

 cause a rupturing force that tends to make fissures in the direction of 

 the bedding more easily produces separations or openings between them 

 than fractures across them — planes in the direction of the bedding 

 being those of weakest cohesion ; or there may be an interrupted 

 series of such openings, those of the series made severally between dif- 

 ferent layers. Some of the largest of granite veins are of this kind, 

 that is, they are conformable for considerable distances to the bedding. 

 Those of Middletown and Portland, Conn., are examples. Such veins 

 often include thin or thick layers or portions of the schistose rock, or 

 may be banded by it. 



Further, in the flexures of a thin -schistose or slaty rock, the lami- 

 nae very commonly become separated, as the leaves of a quire of paper 

 separate on bending it, and thus innumerable thin spaces are made be- 

 tween the leaves, sometimes many to an inch, which subsequently 

 may become filled with quartz or other mineral matter, so that the 

 rock is delicately seamed with veins parallel with the bedding, some- 

 times looking like a fine white ruling. But the same slaty rocks often 

 contain, in other places, large and irregular veins with abrupt expan- 

 sions and contractions, owing to irregularities in the breakings. 



In the language of miners, veins containing ores are called lodes ; 

 the material inclosing the ore is called the gangue ; and the rock out- 

 side of the vein is the country-rock. 



2. Forms. — The forms of veins are exceedingly various. Some of 

 them are illustrated in Figures 116 to 119, and 132, 133, on pages 

 109-112, to which the reader should here turn. They may have (1) 

 parallel walls, or (2) contract and expand irregularly along their 

 course. The latter is the most common condition, but the two may 

 characterize different parts of the same vein. They may (3) make a 

 network through the mass of the rock, so that, if metalliferous, the 

 whole rock is removed to obtain the ore. 



(4.) When large chambers and passages in a rock contain ores, the 

 fillings are often spoken of as veins, even when there is no evidence 

 that the chambers are connected with, or originated in, fractures. 



