130 ME. ALFRED HARKER ON THE CARROCK FEI/L [May 1895,, 



From Mr. Barrow's analysis, in conjunction with the microscopical 

 examination, the mineralogical composition of the granopbyre may 

 be calculated as follows : — 



Si0 2 



Plagioclase. 

 32-90 

 9-75 



Orthoclase. 



13-50 



3-84 



3 53 



Quartz. 

 2096 



Augite. 

 4-24 



215 



021 

 1-97 



Totals. 

 71-60 

 13-59 



FeO .... 





2-15 



MgO 

 CaO .... 



0-33 



0-21 

 2-30 



Ts T a 2 

 K,0 .... 



5-55 



5-55 

 353 









48-53 2087 2Q-96 8-57 9893 



From this it would appear that the plagioclase-felspar of the rock 

 is one of the albite-oligoclase series with a ratio Ab : An = 7"4 : 1, 

 or nearly 15 : 2, its percentage composition being as below. This. 

 however, is only the average composition, and it may well be that 

 the porphyritic crystals are of a more typical oligoclase, while the 

 triclinic felspar which, with the orthoclase, makes the felspathic 

 constituent of the microg'raphic groundmass is a more nearly pure 

 albite, 



Plagioclase. Augite. 



SiO, 67-79 SiO., 49-47 



A1,0 3 20-09 FeO 25'09 



CaO 0-68 MgO 2-45 



Bfa a O 11-44 CaO 22-99 



100-00 100-00 



The augite would appear to be a diopside approaching hedenbergite, 

 the ratio Mg : Fe being 21 : 215, or nearly 1:10; but the calculation 

 is probably of little value in view of the small part which the mineral 

 plays in the rock. It is evident, however, that the augite cannot 

 be of a variety rich in alumina, and this makes another point of 

 contrast with the augite of the eabbro. 



11. Variation observed in the Granophyre. 



Over a large part of its extent the granophyre. of the Carrock 

 Fell intrusion does not seem to vary much from the specimen 

 analysed, and the same is true of the intrusions of Eae Crags and 

 Great Lingy. The highest percentage of silica found was 77*38, at 

 a spot below the Scurth, about 500 yards W.N.W. of Stone Ends 

 farm. 1 On the other hand, portions of the Carrock Fell mass are 



1 The following silica-p?rcentages of different specimens of granophyre I 

 owe to the gentlemen named in my former paper. Those marked S were 

 determined at Sidney Sussex College by Messrs. Brend and Cunningham-Craig, 

 those marked L were determined at Leeds by the pupils of Dr. Cohen : — 



(i) Below Scurth, at 500 yards W.N.W. of Stone Ends : 



Silica 77-38 (S) ; sp gr. 2-607. 

 (ii) In peat-moss S. of Drygill Head : Silica 75 - 3 (L) ; sp. gr. 2-530. 

 (hi) Outcrops 100 yards E. of Carrock Fell summit : 

 Silica 71-60 (Barrow) ; sp. gr. 2-670. 



