Ch. VIII.] THE GRANITIC AND SCHISTOSE ROCKS. 161 



found to resemble the veins, courses, or beds which form an 

 integrant part of the central mass. 



2. The slate which is contiguous to the granite- veins, is 

 frequently much harder, more crystalline, and its texture is, 

 in general, less schistose than that which is more distant : 

 and it often exhibits mica, hornblende, or other minerals in a 

 distinct form, the nature of the mineral depending on the 

 composition of the containing rocks. 



3. Some granite-veins are closely connected with the slate, 

 both being intimately united and inseparable ; and indeed, 

 sometimes, as in the case of Rannoch, one of the component 

 minerals of the veins is crystallised, and its crystals penetrate 

 and are contained in the slate as well as in the vein : it often 

 happens, however, that the veins can be easily detached from 

 the slate, and have distinct walls ; that is, an open seam or 

 joint divides them from the slate. 



4. Detached portions of the slate, having the appearance 

 of fragments, are frequently insulated in the granitic veins, 

 and sometimes indeed also occur in the main body of granite; 

 and, vice versa,, similar portions of granite are often completely 

 enveloped in the slate. 



5. These veins are sometimes so abundantly and intricately 

 blended with the slate, either one or the other predominating 

 in the mass, that the whole is involved in apparent confusion ; 

 whilst in other cases the slate reposes on the granite without 

 any appearance of dislocation or disturbance, and is traversed 

 by well-defined granite-veins. 



6. These veins have, in some cases, been traced to the 

 main mass of granite, with which they appear to be in com- 

 plete union, and to form one body, losing entirely their 

 character as veins ; whilst in other instances these veins have 

 been found to continue their course through the granite as 

 well as the slate. 



7. The granite- veins have no general direction or position ; 

 they run towards every point of the compass, and dip at 

 every angle from the horizon to the perpendicular. 



M 



