72 



BOOK III. 



Lastly, the seams, which are the very finest stringers {fibrae), divide 

 the rock, and occur sometimes frequently, sometimes rarely. From 

 whatever direction the vein comes, its seams always turn their heads 

 toward the Ught in the same direction. But, while the seams usually run 

 from one point of the compass to another immediately opposite it, as 

 for instance, from east to west, if hard stringers divert them, it may 

 happen that these very seams, which before were running from east to 

 west, then contrariwise proceed from west to east, and the direction of 

 the rocks is thus inverted. In such a case, the direction of the veins is 

 judged, not by the direction of the seams which occur rarely, but by those 

 which constantly recur. 



A — Seams which proceed from the east. B — The inverse. 



Both veins or stringers may be solid or drusy, or barren of minerals, 

 or pervious to water. Solid veins contain no water and very little air. The 

 drusy veins rarely contain water ; they often contain air. Those which 

 are barren of minerals often carry water. Solid veins and stringers con- 

 sist sometimes of hard materials, sometimes of soft, and sometimes of a 

 kind of medium between the two. 



