Vol. 62.] BUTTEEMEEE AND ENNEEDALE GEANOPHYEE. 263 



An examination of a series of slices shows that the rock is very 

 far from fresh ; but it was, near the margin [4766], an ophitic 

 augite-dolerite of typical structure. The only ferromagnesian mineral 

 present appears to have been augite, which is now represented by 

 actinolitic hornblende ; epidote, zoisite, calcite, chlorite, etc., are also 

 abundant, derived from ' saussuritized ' felspar. 



Towards the middle of the intrusion [4767] the rock is much 

 fresher, and more acid in character. It contains large idiomorphic 

 crystals of plagioclase, which show extinction-angles corresponding 

 with andesine and oligoclase ; there are also some crystals showing 

 twinning on the Carlsbad law only, which must be identified as 

 orthoclase. The chief coloured mineral is ophitic augite, sometimes 

 replaced by actinolitic hornblende and the usual type of chlorite. 

 A fair proportion of quartz is also present ; and there is a certain 

 amount of groundmass consisting of a beautiful micropegmatite of 

 quartz and felspar. All slices of this rock show apatite and 

 ilmenite as abundant accessories ; the latter is often converted into 

 leucoxene. Epidote, zoisite, chlorite, and calcite are abundant as 

 decomposition-products. 



The outer margin of this rock contains a very high proportion of 

 coloured minerals : in fact, in one slice I estimated them to amount 

 to 75 per cent, of the whole, while at the centre they are much 

 less abundant. 



The facts just stated suggest that the magma has undergone a 

 certain amount of differentiation after intrusion, leading to a concen- 

 tration of basic minerals at the margin ; but this explanation seems 

 insufficient to account for all the phenomena, especially the occurrence 

 of orthoclase and quartz in the pink-spotted middle part. This 

 type shows very strong affinities to the neighbouring granophyre, 

 and it seems probable that its peculiar character can best be ex- 

 plained on the supposition that it is a mixture-rock. According 

 to this view, the basic dolerite was first intruded, and while it was 

 still hot and partly liquid in the middle another injection of more 

 acid character took place from the same source, and penetrated into 

 the still unconsolidated centre of the earlier intrusion, producing a 

 hybrid rock, intermediate in character between granophyre and 

 dolerite. Exposures in the field support this view, and it is in 

 accordance with observations made on the Bowness-Knott mass 

 (p. 265). 



Associated with this basic intrusion are some beautiful examples 

 of acid dykes. One of these runs parallel to the lower margin of 

 the dolerite for the greater part of the length of the exposure, and 

 some distance below it ; perhaps 40 or 50 feet. The other dyke 

 first appears some distance to the east of the eastern extremity 

 of the dolerite, and cuts obliquely across it ; on reaching the lower 

 margin of the dolerite it turns parallel to it, and forms the base of 

 the intrusion, until the latter disappears. The acid dyke, however, 

 is continued westward across the flanks of High Stile, and can be 

 traced into the main outcrop of granophyre on the east side of 

 JBleaberrv Combe. 



