﻿Vol. 66.^ SKIDDAW GRANITE AND ITS METAMORPHISM. 117 



II. The Skidd aw Granite. 



The visible exposures of the Skiddaw granite are three in number, 

 name!} 7 , a smail one in Sinen Gill, which is the northernmost tri- 

 butary of the Glenderaterra valley on the left or eastern bank ; a 

 much larger exposure in the floor of the Caldew valley ; and a 

 third, of fairly large size, near the junction of Grainsgill Beck with 

 the River Caldew. In connection with each of these there is some 

 point worthy of special note, and they may be dealt with in the 

 order above stated. 



So far as can be seen from the very limited exposure, it seems 

 probable that the granite of Sinen Gill is of the nature of a large 

 dyke, an apophysis of the main mass. The junction of its upper 

 surface with the Skiddavian rocks is clearly displayed in the stream ; 

 it is obvious that the junction cuts almost at right angles across 

 the general strike of the district, and it appears to dip steeply to 

 the east. Hence it cannot be either a sill intruded along the 

 bedding planes, or a portion of the upper surface of a laccolith, as 

 is probably the case with the larger exposures. Also, so far as my 

 observations go, the size of the exposure seems to have been greatly 

 exaggerated. It is highly improbable that the granite extends so 

 far south as is indicated on the published maps of the Geological 

 Survey. In these granite is shown at the surface nearly as far as 

 Roughten Gill, but there is no evidence for this. On the contrary, 

 to judge by the low grade of metamorphism in Roughten Gill, it 

 would seem that the rocks here are at a considerable distance from 

 the margin of the granite. Unfortunately there are no exposures 

 in the lower part of the ridge separating the two gitls, so the- 

 question cannot be definitely settled. At all events, nothing re- 

 sembling the intensely altered, so-called ' mica-schist ' of Sinen Gill 

 is to be seen in Roughten Gill, even at the point where the frequent 

 exposures in the stream ought, according to the published maps, to> 

 lie close to the granite ; and even the second grade of alteration is. 

 hardly attained. The northward extension of this exposure of 

 granite is even less defined, as no rock in situ is seen on the hillside 

 for a long distance north of Sinen Gill: the whole is covered by a 

 thick mass of moss and peat overlying drift. It may be summarily 

 stated that the only certain fact is the occurrence of a thick mass 

 of granite in the bed of Sinen Gill ; the upper margin is clearly 

 seen, but the lower margin is very much a matter of inference. It 

 follows that we have no real means of judging of the form of this 

 intrusion ; but, in all probability, it is a thick inclined sheet, or dyke, 

 cutting obliquely across the bedding, and forming an apophysis of a 

 mass which is continuous with the larger exposures in the Caldew 

 valley and near Grainsgill. 



The second exposure is of much greater extent, and of a very 

 different character; it covers an area of about a mile from east to 

 west and half a mile from north to south, forming a large portion 



