16 



ECONOMIC GEOLOGY 



branches. This is especially true as a vein passes from the sedi- 

 mentaries into the associated intrusives (Fig. 13). 



\ 



\ 



FIG. 15. Ore bearing quartz vein, somewhat lens-shaped. The country 

 rock is altered, but contains no ore. (After Lindgren.) 



(2) Veins often dividing may come together as one vein and 

 enclose a portion of the country rock. Such an enclosed portion 

 is called a " horse." Several masses of rock may appear within 



FIG. 16. A vein brecciated on one side and banded on the other. 



the vein and then they are called a "troop of horses," as shown 

 in Fig. 14. 



