126 MR. ALERED HARKER ON THE CARROCK FELL [May 1895, 



about Eae Crags, farther north-west, probably belong to a mass 

 distinct from the preceding, separated from it by diabase, and faulted 

 on the north against the Eycott Hill lavas and the Drygill Shales. 

 Granophyre is seen at certain points on the moorland of which Great 

 Lingy is the centre : if these outcrops belong to one connected mass, 

 its extent from Boughten Gill eastward must be nearly 2 miles. 

 There are smaller intrusions in Arm o' Grain and other gills, but we 

 may confine our attention chiefly to the mass first indicated, which 

 is well exposed about Carrock Pell and the Pike and in the cliffs 

 known as the Scurth. 



The question of the geological age of the granophyre and the 

 slightly earlier gabbro is one bound up with the interpretation of 

 the general structure of the Lake District, and must be very briefly 

 dismissed in this place. The rocks have been intruded at the 

 junction of the Skiddaw Slates and the Eycott Hill lavas since these 

 two groups assumed their present mutual relations. There is reason 

 to believe that these relations are not the natural ones, and that the 

 absence here of certain other groups which should intervene is a 

 result of the great post-Silurian crust-movements. If this be so, 

 the intrusions must be later than these crust-movements. The 

 absence of cataclastic structures or any phenomena attributable to 

 shearing in the intrusive masses is, so far as it goes, a confirmation 

 of this view. The faults which have displaced the intrusive rocks 

 are to be referred to the later (post-Carboniferous) system of .dis- 

 turbances, with which the metalliferous lodes of the region in general 

 seem to be connected. 



10. Description oe the Granophyre. 



Before considering the variation exhibited by the Carrock Fell 

 granophyre, a short description must be given of what we may regard 

 as the normal type of the rock. It is essentially an augite-grauo- 

 phyre, the mineral named being always present and being the only 

 ferro-magnesian constituent of the rock. 



The only common accessory mineral is zircon, which is very 

 generally distributed in small prisms with square cross-section. 

 A little original magnetite occurs in a few slides, but is never 

 prominent. 



The augite of this rock presents a strong contrast to that of the 

 gabbro. It builds crystals sometimes showing a good octagonal 

 cross-section, more usually rather rounded and irregular, but always 

 idiomorpbic towards the felspar. The fresh crystals are of a pale 

 to deep green tint in slices, but the mineral is commonly more or 

 less completely replaced by a green decomposition-product of chloritic 

 or perhaps serpentinous nature. This is strongly pleochroic, the 

 absorption- colours changing from bluish-green to greenish-yellow : 

 its birefringence seems to vary considerably. Uralitization is also 

 observed in many of the slides. 



The frequent association of augite with granophyric structures in 

 our British rocks is a point worthy of passing notice. It is observed 



