42^ 



Remarks on the 



It was first stated tliat they were formed of newer granite, and 

 if properly examined would be found to cut the old granite as 

 well as the rock which rested on it. This opinion was once very 

 strenuously supported in this country ; but as facts would not 

 bear it out it was abandoned. I find, however, in a recent pub- 

 lication, something similar to it maintained by de Luc, who 

 asserts that the veins at St. Michael's Mount are not granite, 

 but merely quartz, v»/hich traverses the granite as well as the 

 stratified rock. I cannot comprehend how de Luc could have 

 been so much deceived at this place, as simple inspection of the 

 smallest specimen will prove that he was mistaken. 



It was next said that the veins in question were not true veins^ 

 but such as are termed cotemporaneous. To support which it 

 was boldly asserted that they never extended beyond the limits 

 of such rocks as were composed of the same materials, gneiss^ 

 and mica- slate. 



I trust it is now distinctly shown that they do extend beyond 

 these limits, and likewise that they traverse rocks from which 

 by no method of reasoning, it can be supposed that they could 

 possibly be formed by secretion. 



The last opinion is that which has recently been brought 

 forward by Dr. Berger.* After describing the granite veins of 

 St. Michael's Mount, he proceeds to say, that they are simply 

 elevations on the plane of the granite existing previous to its 

 being covered by the stratified rock ; that the spaces between 

 them were filled up as the greywacke was deposited ; and hence 

 the abrasion of the surface brought to light a section which has 

 merely an appearance of veins. Were the devotion of Dr. 

 Berger to his master less conspicuous in his geological disquisi- 

 tions, I should be inclined, on the above statement, to call his 

 character as an observer in question, having passed over in 

 silence the detached masses of killas, vvhich he could not fail to 

 observe included in the granite, and which the above hypo- 

 thesis is as far from accounting for as either of those mentioned 

 before. 



I have only a few specimens to lay before the Society from the 

 veins of St. Michael's Mount; but they are equally interesting 

 and satisfactory. One exhibits a portion of the killas bounded 

 on each side by granite ; another, a portion of two granite veins 

 traversing killas ; and the third, a mass of killas included in the 

 granite. Simple inspection is sufficient, in the first place, to 

 show that the opinion of de Luc is groundless with respect to 

 the substance of these veins. One of the specimens also con- 

 tains two small veins of quartz, which are of the kind called 

 cotemporaneous ; these keep the direction of the seams of the 



* Transactio;is of tise Geological Society, vol. i. p. i4To 



