Remarks on Dr. Boase's Primary Geology. 553 



" 1 . The composition of the granite-veins is generally different from 

 that of the main body of granite, and it is very frequently of a much 

 smaller grain. It will, however, be 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 frequent- 

 ly 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 latter. 



" 4. Detached portions of the slate, having the appearance of frag- 

 ments, are frequently insulated in the granitic veins, and sometimes 

 indeed also occur in the main body of granite ; and, vice versd, similar 

 portions of granite are often completely enveloped in the slate. 



" 5. These veins are sometimes so abundantly and intricately blend- 

 ed 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 complete 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. 



" 8. These veins are sometimes straight, and pretty regular in their 

 thickness ; but in general they are more or less tortuous, and 

 gradually become smaller as they recede from the granite. 



