Vol. 65. J 1ST THE NEIGHBOURHOOD OF ESKDALE. 67 



Stony-Tarn area. — In this area (129), near the margin of 

 the granite, occurs a granitoid rock which is distinctly porphyritic 

 in appearance. The phenocrysts are of quartz and muscovite, and 

 the ground-mass is a microcrystalline aggregate of quartz, felspar, 

 muscovite, and biotite. The rock is, in fact, a quartz-porphyry. 



Between Goat Crag and Whin Crag (130, 131, & 132) is a good 

 exposure of the junction-breccia, of which fig. 3 is a photograph ; 



Fig. 3. — Junction-breccia near Stony Tarn. 



[The white veins are of marginal granite, and penetrate a dark andesitic lava.] 



while fig. 4 (p. 68) represents a hand-specimen of the same rock 

 collected at 131, PI. Ill, fig. 5 illustrating a thin section of the 

 same. 



The Borrowdale rock was apparently a porphyritic andesite 

 before alteration. The ground-mass now consists of minute flakes 

 of brown, slightly pleochroic biotite, with a little muscovite, felspar, 

 and quartz. The phenocrysts of pyroxene have been converted 

 into a meshwork of pale amphibole, with a little secondary quartz. 

 A pale pyroxene also occurs in smaller quantities. A few pheno- 

 crysts of felspar have been altered, and now contain flakes of 

 muscovite. 



The granitoid rock is a fine-grained mosaic of quartz, containing 

 in the broader veins phenocrysts of quartz, orthoclase, and oligoclase. 



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