198 GRANITES AND GRANITIC VEIN-STONES. [XL 



They are sometimes transverse to the stratification, but more 

 often parallel, and, standing above the soil, are very conspicu- 

 ous. 



21. We have already noticed the exotic granites of Bidde- 

 ford, which are intruded among fine-grained bluish or grayish 

 silicious strata. These latter are traversed by numerous veins 

 of endogenous granite, which are very unlike in aspect to the 

 intrusive rock. One of these veins, near Saco Pool, has a 

 diameter of about an inch and a half, and presents on either 

 wall a layer of yellowish crystalline feldspar about one fourth 

 of an inch in thickness, which includes long plates of dark 

 brown mica. These penetrate the central portion of the vein, 

 which is a broadly crystalline bluish orthoclase, enclosing 

 small portions of quartz, after the manner of a graphic granite. 

 The yellowish and less coarsely crystalline feldspar, with its 

 accompanying mica, had evidently lined the walls of the vein 

 while the centre yet remained open, and had moreover entirely 

 filled a small lateral branch. The same conditions are seen in 

 the filling of other veins in this vicinity, which are often much 

 larger, and present upon their walls bands of an inch or two 

 of the yellowish feldspar, with mica. 



The successive filling of a granitic vein is still more clearly 

 shown in a specimen from Sherbrooke, Nova Scotia, which I owe 

 to the kindness of Professor H. Y. Hind. The vein, which is 

 seen io be transverse to the adherent fine-grained mica-schist, 

 has a breadth of nearly four inches, about two thirds of which 

 is symmetrical, and is included between two layers, perpendic- 

 ular to the walls, consisting of a fine-grained mixture of white 

 feldspar and quartz, each about one fourth of an inch thick, 

 and marked by subordinate zones, more or less quartzose. 

 Within these two bands is a coarser aggregate, consisting of 

 two feldspars', with some quartz and muscovite, plates of which, 

 and crystals of pink orthoclase, penetrate an irregular layer of 

 smoky quartz varying from one eighth to one half an inch in 

 diameter. This fills the centre of the symmetrical portion of 

 the vein, on one side of which is the mica-schist, while the 

 other is bounded by a band of more than half an inch of fine- 



