﻿Vol. 66.~] SKIDDAW GRANITE AND ITS METAHOBPHTSM. 135' 



Towards the south-west the outcrop of grits becomes narrower, 

 and appears to sink underground below the higher parts of 

 Skiddaw. The grits have not again been recognized with certainty 

 on the western side of this mountain, where grey and black slates 

 are predominant. 



In a careful and detailed examination of the ground, one of the 

 most striking features is the much greater intensity of the meta- 

 morphism at the north-eastern corner, as compared with the rest. 

 The altered rocks here come into contact with the igneous complex 

 of Carrock Fell, and at first sight it might be supposed that this 

 great intrusion was responsible for the higher degree of alteration 

 here observed. But a very cursory examination suffices entirely to 

 disprove this idea. The contact between the gabbro and the 

 sedimentary rocks can be followed closely all the way up the 

 Caldew valley from Mosedale to Grainsgill, and beyond, a distance 

 of over 2 miles. According to the officers of the Geological Survey 

 and to Mr. Harker this junction is a faulted one, but there is no 

 evidence on the ground in favour of this supposition. On the hill- 

 side, a few yards above the village of Mosedale, the actual contact of 

 grit and gabbro is very clearly seen, and the grit is practically 

 unaltered. It may be mentioned in passing that it is possible here 

 to collect small hand-specimens showing grit and gabbro completely 

 welded together, which is inconsistent with the idea of a faulted 

 junction. As we follow the contact along the side of Carrock Fell 

 towards Grainsgill the grit gradually becomes increasingly meta- 

 morphosed, until near the farm of Swinside the alteration is 

 intense, and so continues up to the outcrop of the granite rocks. 

 This clearly shows that the alteration is progressive in a direction 

 parallel to the edge of the gabbro, and perpendicular to that of the 

 granite ; it is therefore clearly due to the latter alone, and in the 

 study of the metamorphism of this region the Carrock Fell complex 

 is a negligible factor. 



In explanation of the greater intensity of the alteration in this 

 part of the aureole, it is significant that the granite of Grainsgill 

 has been largely converted into a greisen by pneumatolytic 

 processes, and the whole of this district is extensively permeated 

 by mineral veins. It may be suggested that the residual vapours 

 and liquids of the granite magma acted more especially and effici- 

 ently on the rocks of this area, and produced a more extensive 

 alteration here than elsewhere. 



The Caldew-Grainsgill section. — As before mentioned, a 

 series of specimens were collected from the bed of the Biver Caldew 

 and from Grainsgill Beck, as nearly as possible in the direction of 

 strike. These range from the first field west of Swinside, up to 

 the actual contact of grit and greisen in Grainsgill, a total distance 

 of about three-quarters of a mile. On the whole, all these are 

 very similar, and the amount of mineralogical change shown in 

 microscope-sections is much less than would be expected from the 

 appearance of the specimens to the naked eye. This is doubtless 



