318 MESSRS. A. HAEKER AND J. E. MARR ON 



limit of the aureole of raineralogical metamorphisin is rather sharply 

 defined. AVhile the tlags seen nearest the Hotel have undergone no 

 important alteration, specimens at no great distance from them, 

 and about 1220 yards from the granite-boundary, show very con- 

 siderable modifications. The carbonaceous matter has been entirely 

 dissipated by " ignition," unless indeed it be partly represented by 

 some of the black granules scattered through the rock. We cannot 

 be sure that some of these are not graphite, and the flaky form of 

 many of them renders it probable ; but others are certainly mag- 

 netite, and by their tendency to crystal outline suggest a meta- 

 morphic origin. The chief authigenetic mineral, however, is brown 

 mica, which is disseminated in minute flakes throughout the whole 

 mass of the rock. The character of the ground, showing very 

 minute granules of quartz and apparently felspar, is more evident ; 

 but this may be due rather to the removal of the opaque organic 

 matter than to any real change in the other constituents. The 

 more easily visible angular grains of clastic quartz, at least, have 

 remained unaltered [1221]. 



Nearer to the granite (at 870 yards) the brown mica forms flakes 

 slightly larger and more distinct, while the general ground of the 

 rock gives clear evidence of recrystallization. In the little streaks 

 where this is best seen, there is a fine-grained aggregate of grains 

 which may include felspar as well as quartz, and the authigenetic 

 character of this aggregate is sufficiently proved by its mosaic 

 arrangement, its limpid appearance, and especially the manner in 

 which it moulds and encloses the mica. In other parts of the slide 

 the nature of the very fine-grained mass, obscured by the mica, is 

 not to be made out with certainty [1220]. There are still evident 

 angular quartz-grains of detrital origin. The opaque grains belong 

 to a yellow pyrites-mineral which seems to be pyrrhotite. 



[We are indebted to the kindness of Mr. W. Maynard Hutchings 

 for drawing our attention to the occurrence of anatasein a specimen 

 from Wasdale Beck. The mineral occurs in groups of very minute 

 crystals in the clearer spaces of the rock, and is conspicuous under 

 a high power by its very high refractive index and birefringence 

 [1327]. Owing probably to the total-reflection border, the crystal 

 form is seen in only a few of the crystals. It appears to be the 

 simple pyramid, or but slightly modified. The straight extinction 

 and the character of the double refraction (<.>>e) agree with anatase, 

 and there is but little doubt of the identity of the mineral. Purther, 

 it seems to be formed at the expense of rutile, for Mr. Hutchings 

 points out that the " clayslate-needles," which he finds in the less 

 metamorphosed flags lower down the beck, are here almost absent. 

 The locality of the specimen is apparently about 800 or 900 yards 

 from the granite-outcrop. — March 11th, 1891.] 



Still approaching the granite, we come on to the spotted or 

 "knotted" rocks. A specimen taken at 500 yards from the contact 

 does not materially diff'er, except as to the spots, from the last, the re- 

 crystallized mosaic, in which some rectangular sections clearly point 

 to felspar, being visible only in some portions of the slide, while the 



