172 Proceedings of the Royal Physical Society. 



degree of metamorphism and the absorption of felspar, when 

 in a soft state through heat, into gneiss ; and, finally, by 

 absolute fusion with the felspar, into granite. All these 

 gradations are seen here in the most instructive manner, and 

 in every variety. 



The Peterhead granites are chiefly composed of red felspar 

 and quartz, the mica being very subordinate. They are 

 occasionally fine-grained and light grey, like the Aberdeen 

 granite, and enclose numerous fragments of schists. At one 

 place, upon the shore, near Peterhead, a dyke of very beau- 

 tiful flesh-coloured felspar, about twenty-four yards wide, 

 runs E. by S. to W. by 1ST. This is occasionally granitoidal. 

 Near this is a large mass of felspar or felspar porphyry, con- 

 taining veins and nests of quartz. Along this part of the 

 shore the felspar rock is more abundant than the granite. 

 It is also met with in the Stirlinghill quarries. The Aber- 

 deenshire granites appear to be simply the result of the in- 

 vasion, upon a large scale, of the primary schists and quartz 

 rock, by this standard igneous rock. The nature of the re- 

 sulting granite depends wholly upon that of the associated 

 schists. 



To the foregoing examples many others might be added, 

 but those given have been selected on account of the clear 

 and instructive character of the junctions, and their compara- 

 tively ready accessibility. Fassney Water and Glen Tilt, 

 both classic in geology, might have been added ; but as this 

 paper has already exceeded the limits intended, it would 

 be improper at present to enter at greater length upon 

 the subject, although it is one admittedly of very high 

 interest. The writer trusts that his labours in this field 

 may induce other and more competent observers to examine 

 and thoroughly test the correctness of his investigations, 

 by a direct appeal to the rocks themselves. He would par- 

 ticularly impress upon observers the importance of taking 

 notes of the positions of the divisional planes of the granites 

 and porphyries, and comparing them with the directions of 

 the planes of stratification of the nearest rocks of aqueous 

 origin. 



