110 



LITHOLOGICAL GEOLOGY. 



Fig. 119. Two veins a a', presenting some of the common irregularities of mineral 

 veins in size, the enlarged parts containing mostly the ore: a is faulted by another 

 vein b, which is therefore of subsequent formation, but not necessarily long subsequent. 



Figs. 120, 121, 122. Examples of granitic veins of very large size, in a gneissoid 

 granite, showing their subdivisions and various irregularities (taken by the author 



Fig. 122. 



from granitic rocks near Valparaiso). The veins undergo constant changes of size, 

 and in some places encircle masses of rock resembling the rock outside The rock ad- 

 joining the vein is more micaceous than that at a distance, and the direction of the 

 lamination (as indicated in the figures) varies with some reference to the intersecting 

 veins, curving approximately parallel to the veins on two opposite sides, m and n, and 

 not at all so on the other two, o and p. The subdivisions of the veins in Fig. 121 cross 

 one another in an alternate manner, a cutting d and e, but cut by c, and b cut by c, d, 

 and e ; in 122, although the veins are similar in constitution, one cuts the other ; and, 

 in 120, the two crossing veins are broken and subdivided at the intersection, so as to 

 appear like one vein stretching off in two directions, like a letter X. 



