860 



THE WONDERS OF GEOLOGY. 



Lect. VIII. 



state among secondary strata, the latter are invariably 

 altered near the line of junction : but when consolidated 

 masses of granite have been protruded, no such change is 



...,- 



3 4 



Lign. 196. — Intrusions op Trap, Granite, Porphyry, &c. 



Fig. 1. Granite veins (a, a,) traversing schist, Isle of Arran.* 



— 2. Veins of granite (a, a,) traversing schist, themselves crossed by veins of two 



different kinds of porphyry {b, b, b). 



— 3. Gneiss (6, 6, b, b,) shifted by a granite vein {a, a, a). 



— 4. Intrusion of trap between layers of sandstone (a, a), presenting an example 



of fracture and displacement so small, as to admit of the readaptation of 

 the separated portions. t 



observable. Into the slate rocks of the Cumbrian chain, 

 syenite, porphyry, and greenstone, have been injected in a 

 melted state, and now fill up fissures produced during the 

 general movements of those strata ; but the central nucleus 

 of primary rock exhibits no such appearance. 



* Phillips, Encycl. Metrop. 



f Dr. Macculloch, Geolog. Trans, and Western Isles. 



