THE SHAP GRANITE AND ASSOCIATED ROCKS. Jilo 



may bo termed '^ lime-augite." It is evidently the mineral which gives 

 the greenish tint to hand-specimens of the rock, and is apparently 

 identical with the pyroxene which occasionally occurs in the meta- 

 morphosed andesites. It is usually a conspicuous element in slices 

 of the altered Upper Limestone and Calcareous Breccia (see PI. XII. 

 fig. 4). 



The other pyroxene, completely colourless in the sections, has a 

 considerably lower refractive index and rather less double refrac- 

 tion. Sections showing one marked set of cleavage-traces ex- 

 tinguish parallel to these traces. Taking account of all its proper- 

 ties, this mineral may be referred with some confidence to wollaston- 

 ite. It is less abundant than the augite, and does not occur in 

 larger crystals such as those in the radiating nests and tufts of the 

 latter mineral. In some slides it is the dominant pyroxene [872], 

 in others it occurs in smaller quantity associated with the augite 

 [874]. 



We have not found garnet in the metamorphosed Upper Lime- 

 stone. A mineral probably referable to idocrase (?) occurs in one or 

 two slides [1217], but never in the abundance which characterizes 

 the metamorphosed Lower Limestone. Felspar is a common con- 

 stituent, in groups of irregular crystal-grains or occasionally in 

 ophitic plates moulding the augite, &c. It has the water-clear 

 appearance common to the authigenetic felspars of all these meta- 

 morphosed rocks, and the crystals are more commonly simple than 

 twinned. Judging by extinction-angles observed in the twinned 

 crystals, both acid and basic felspars occur : some are certainly to be 

 referred to anorthite. Quartz seems to be present only sparingly in 

 these rocks, but in the very fine-grained parts it is not easy to dis- 

 criminate between this mineral and felspar, and the analysis given 

 below proves that a certain amount of free silica is present. 

 Some slides of the Calcareous Breccia contain a considerable amount 

 of brown mica, usually in small flakes of a pale colour [1214, 1215, 

 1216], and there are some little veins of pale yellow pleochroic mica 

 with clear quartz [1213]. A grain or two of magnetite is seen only 

 very rarely [874]. 



It will be seen from the above brief account that the Wasdale 

 Head section afi'ords some interesting examples of highly-metamor- 

 phosed calcareous rocks. The beds here exposed have evidently not, 

 for the most part, been of the nature of pure limestones. The con- 

 siderable amount of alumina represented by the garnets and idocrase 

 in the "Lower Coniston Lim.estone " at this locality clearly points 

 to the former abundance of ashy material in the strata ; they were 

 probably calcareous shales or fine ashes, like those which are seen 

 at Stile End and constitute the usual fades of this subdivision. The 

 Upper Limestone, in so far as it is represented at this spot, must also 

 have been impure, and was probably to some extent dolomitized. 

 Indeed, Mr. Garwood finds these porcellanous-looking rocks to be 

 rich in magnesia as well as in lime. The following analysis of an 

 average specimen of the metamorphosed Upper Limestone probably 

 gives a fair idea of the constitution of the altered rocks of this divi- 



