
Parr VIL Secor. i. §1.] ERUPTIVE GRANITE. 543 
granite. Occasionally granite-veins protrude from the main masses, but 
in the metamorphosed zone which surrounds the Criffel granite area in 
Kirkeudbright, hundreds of dykes and veins of various felsitic or elva- 
nitic rocks occur. 
Sinilar features are presented by the granite bosses of Devon and 
Cornwall, which have been risen through Devonian and Carboniferous 
strata. ‘lhe Dartmoor mass is specially instructive. As shown by the 

Fic, 271.—Puan or GRANITE Boss, CAIRNSMORE OF FLEET, SCOTLAND, 
The granite area (c) is from 7 to 10 miles in diameter, rising through highly inclined 
Lower Silurian strata (a), among which are some conspicuous bands of black an- 
thracitic and graptolitic shales (0). The arrows show the direction of dip; the 
parallel lines that of the strike. The ring within the dotted line round the granite 
defines the belt of metamorphism. 
early work of De la Beche, it passes across the boundary between the 
Devonian and Carboniferous areas, extending chiefly into the latter, so 
that it cuts across strata of different ages. In doing soit has risen 
irresistibly through the crust without seriously affecting the general 
strike of the rocks. It cuts off the ends of old volcanic bands, and of 
associated grits and shales into which it sends veins.” 
1 Round the marginal portions of many granite bosses 
the rock abounds in such crystalline enclosures (p. 133). 
The more angular and irregularly shaped of these, 
evidently portions of the surrounding rocks caught up in 
the granite, are commonly fragments of mica-schist, 
gneiss, &c., retaining their foliation, which may have 
been developed in them after their disruption and en- 
closure in the granite. Other rounded concretions and 
cavities lined or filled with crystals are due to irregular 
segregation in the mass of granite. Examples of this 
nature occur in the Cornish and Devon granite, as in 
Fig. 272, which is cited by De la Beche as showing a 
central cavity (a), not quite filled with long crystals of 
schorl surrounded with an envelope of quartz and schorl 
(0), outside of which lies a second envelope of the same 
minerals, the schorl predominating, the whole being 
contained in a light flesh-coloured and markedly felspathic 

Fig. 272.—CRYSTALLINE GEODE 
granite. See a paper by J. A. Phillips, Q. J. Geol. Soe. iN GRANITE, DARTMOOR 
Meaxxvi. p. 1. (B.). 
2 De la Beche, “‘ Report, Devon and Cornwall,” p. 165. 
