﻿124 ME. E. H. EASTALL ON THE [^V I9IO, 



as at present exposed, pass over the summits of these mountains, 

 thus strongly accentuating the basin-like form of the whole. There 

 <5an be no doubt that the highly altered cordierite and andalusite- 

 rocks of the inner part of the aureole, in which bedding and 

 cleavage have been completely obliterated, should present much 

 greater resistance to the ordinary agents of denudation than the 

 •cleaved slates and well-jointed grits of the normal unaltered Skiddaw 

 Series ; but it is clearly evident that they do not, and it is im- 

 possible at present to offer any reasonable explanation of this 

 curious anomaly. 



The altered area surrounding the Skiddaw granite is an un- 

 usually large one, and out of all proportion to the visible exposures of 

 igneous rock. It is generally admitted, therefore, that a large mass 

 •of granite must underlie the whole district at a comparatively small 

 depth. The aureole is roughly circular in form, and has a maximum 

 •diameter from east to west of nearly 6 miles ; the diameter from 

 north to south is slightly less, being about 5 miles. Unfor- 

 tunately, over a large part of this extensive area the exposures are 

 very poor, owing to great accumulations of drift and peat. This is 

 particularly the case in the upper and wider part of the Caldew 

 valley, between Grainsgill and Skiddaw House ; the northern flank 

 of Saddleback also is almost completely covered by a great mantle 

 of drift bearing thick grass, and exposures here are very few and 

 far between. The only exposures with any pretence to continuity 

 are in the streams which run into the Caldew : Blackhazel Beck, and 

 one or two others on the south side, and Wiley Gill, Burdell Gill, etc. 

 on the north. In most of these the junction of granite and sedimen- 

 tary rocks is fairly well seen. Another district which presents 

 special difficulties is the western face of Skiddaw : the outer margin 

 of the aureole runs far below the summit on this side, over the 

 enormous screes which are so conspicuous a feature of the upper 

 part of this mountain, and it is consequently very difficult to follow 

 and map accurately. For these reasons many of the lines shown on 

 the accompanying map (PI. XIV) must be regarded as approximate 

 •only. 



IV. The Metamoephtsm. 



Although this is so well-known an example of metamorphism, 

 no complete account of the phenomena has ever been published, 

 -and the only description of any length is that contained in Clifton 

 Ward's memoir. 1 Some of the conclusions to which he came were 

 soon after controverted by Rosenbusch. 2 At that time microscopic 

 petrography was in its infancy, and the whole subject has never yet 

 been investigated by modern methods, although a few notes on minor 

 points have been published from time to time. 



1 ' The Geology of the Northern Part of the English Lake District' Mem. 

 ■Geol. Surv. 1876, pp. 5-12. 



- 'Die ISteiger fechiefer' 1887, p. 211. 



