Vol. 65.] IN THE NEIGHBOURHOOD OE ESKDALE. 59 



this fact may perhaps, considering that the two rocks are of some- 

 what similar composition and similarly circumstanced as regards 

 exposure, be taken as indicating that the granophyre is the newer 

 rock. There is, however, at present no direct evidence as to the 

 relative ages of the two intrusions, and I fear that this could not 

 he gained without somewhat extensive excavations. 



The Upper Surface of the Granite. 



It is a fortunate circumstance that the whole of the covering of 

 Borrowdale rocks has not been denuded from the granite, and the 

 outliers on the summits of Blaetarn Hill and Great Barrow provide 

 a means of determining the form of the upper surface of the 

 intrusion. The granite shows marginal characters in both these 

 cases, the hills being capped by Borrowdale rocks. At Great Barrow 

 the outlier is faulted on the eastern side, and the Borrowdale rocks 

 dip south-eastwards at an angle of 20°. 



The relations of these outliers to the granite and to the general 

 mass of the Borrowdale rocks will be made clear by a reference to 

 the sections (figs. 1 & 2, p. 60), which are drawn to true scale. 



It is interesting to note that on the crest of the granite-mass 

 the Borrowdales are frequently reduced to a state of breccia, the 

 interstices between the angular blocks of the lava and ash being tilled 

 by a rock identical with the marginal phase of the granite. This 

 points to the intrusion having produced a disruptive effect along its 

 highest part. This breccia is not seen along the flanks of the 

 granite, although even here the volcanic rocks are penetrated for 

 many feet by small veins of granitoid matter. 



It w T ill be noticed, on reference to the published 6-inch maps of 

 the Geological Survey, that the Borrowdale rocks dip away from the 

 axis of the granite-mass as though they had been elevated into a 

 dome by its intrusion. Further evidence of the laccolitic nature 

 of the intrusion is to be found in the fact lhat the granite becomes 

 increasingly acid as its margin is approached, in some instances 

 approximating in composition to pure quartz. The rocks into 

 which the granite has been intruded are in every case of inter- 

 mediate composition, consisting of andesitic lavas, ashes, and 

 breccias ; and, if marginal absorption of the surrounding rocks had 

 taken place, even to a slight extent, one would have expected a 

 higher proportion of the basic matter in the marginal varieties 

 than in the normal granite more remote from the edge, whereas 

 the opposite will be shown to be the case. 



The junction-specimens which have been collected and those 

 which have been examined in the field, show a clean-cut line of 

 demarcation between the intrusive quartz-rock (marginal granite) 

 and the Borrowdale rocks ; and, even when examined in thin sections, 

 the junctions are perfectly sharp, nor is there the slightest sign 

 of any absorption of the andesites having taken place. 



It is, therefore, supposed that the Borrowdale rocks were cold 



