Part VIL Sect. i. §3.] SEGREGATION VEINS. Se 5ST 
they traverse, though the reverse is frequently the case, more 
especially in granite. Close examination of them shows that instead 
of being sharply defined by a definite junction line with the en- 
closing rock, they are welded into that rock in such a way that they 



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Fic. 283.—SEGREGATION VEINS IN DIABASE. 
cannot easily be broken along the plane of union. This welding is 
found to be due to the mutual protrusion of the component crystals 
of the vein and of the surrounding rock—a structure sometimes 
admirably revealed under the microscope. Veins of this kind 
evidently point to somé process, still unexplained, whereby into rents 
Wea 
RD 
eh: Mi Hy 


HONS 
IRB 
fH Wy 
Dig ah adel 
a 
is ity ay! ne ; 
co 
SER 
~ 
es 
= SSS 
SSS 
~ 
Fic. 284.—PEGMATITE VEIN ASSOCIATED WITH FoLIATED GRANITE. RUBISLAW QUARRY, 
ABERDEEN. ‘ 
g g, Ordinary granite of the mass; p p, coarse pegmatite veins; s s, foliated granite 
passing insensibly into g; q, mass of quartz. The black patches in p and q are 
nests of schorl. 
formed in the deeply buried, and at least partially consolidated or 
possibly colloid mass, there was a transfusion or exosmosis of some of 
the crystallizing minerals. Along the margin of segregation veins in 
eranite a foliated structure of the rock may be occasionally observed, 
as in some of the large granite quarries near Aberdeen (Fig. 284). 
