﻿116 . ME. K. H. EASTALL ON THE [May I9IO, 



6. The Skiddaw Geanite and its Metamoephism. By E. H. Rastall, 

 M.A., F.G.S., Fellow of Christ's College, Cambridge. (Read 

 December 15th, 1909.) 



[Plate XIY— Map.] 



Contents. 



Page 



I. Introduction 116 



II. The Skiddaw Granite 117 



III. The Metamorphic Aureole 121 



IV. The Metaraorphism 124 



V. General Conclusions 137 



I. Introduction. 



The main object of this paper is the investigation of the alteration 

 of the sedimentary rocks of the Skiddavian Series by the intrusion 

 of the mass of igneous rock which is commonly known as the 

 Skiddaw granite. One or two cognate subjects will be touched 

 upon, such as the composition and petrographical character of 

 the intrusion, and the general structure and tectonic relations of 

 the sedimentary series ; but, in the main, the paper is a study in 

 metamorphism. The Skiddavian Series includes rocks of varying 

 lithological character, grits, flags, shales, and slates, so that the 

 products of metamorphism are not by any means uniform in 

 character ; and, in addition to this, the problem is complicated by 

 the occurrence throughout the area of a varying though generally 

 high degree of folding and cleavage. Hence it is necessary to study 

 the effects of thermal metamorphism superposed upon those of a 

 previous dynamic metamorphism. 



During my examination of the Buttermere and Ennerdale grano- 

 phyre, I was naturally led to study the effects of this intrusion on 

 the surrounding rocks, which are well-marked. This subject proved 

 to be an unusually difficult one, and I then turned my attention to 

 the metamorphism of the Skiddaw intrusion, in the hope that this 

 would throw some light on the puzzling phenomena presented in 

 the former case. It seemed advisable, therefore, to make a complete 

 study of the Skiddaw metamorphism ; and since this latter is in 

 itself the more important case, and probably the more instructive 

 from a general point of view, the results are here presented. This 

 investigation has been assisted by a grant from the Government 

 Grant Committee of the Eoyal Society, which has defrayed the 

 cost of the very large number of rock-slices that were found 

 necessary. 



