192 ON THE VEINS IN PRIMARY ROCKS. [Ch. IX- 



the rock changes ; they are not straight, but are curved both 

 in their course and dip ; their sides or walls are only distinct 

 from the rock when the seams or joints are developed by de- 

 composition, and are always partially confounded with the 

 rock by a perfect intermixture or transition ; they intersect 

 each other both in length and depth, and in the larger veins 

 those series which run in the same direction are generally 

 affected by the others in a similar manner ; but this is not 

 invariably the case : their intersections are very frequently 

 attended by alterations in the course of the disconnected 

 veins, but the amounts of these apparent movements, in an 

 extensive series, are very various, even in the case of a single 

 intervening vein. 



