ASSOCIATED METAMOKPMC KOCKS OF THE LAKE-DISTRK!T. 593 



the granitic appearance sometimes comes on at a considerable dis- 

 tance. Thus, certain of the coarse ash-beds of Slight Side (Scawfell), 

 a mile from the nearest granite seen at the surface, have a very- 

 granitic look at a little distance, weathering in the same sort of way ; 

 and it is sometimes almost impossible to draw any definite line 

 separating the undoubted but yet highly altered coarse ash or 

 breccia from a distinctly crystalline rock verging on a good typical 

 granite (Example, East side of Great Moss, head of Eskdale). 



What has been here said is true of both Eskdale and Shap 

 granites ; but in the case of the latter the metamorphism has neither 

 spread so widely, nor are there any undoubted cases of outlying 

 patches of what may be called bastard granite, such as occur about 

 Scawfell Pikes near the Wastdale and Eskdale granitic masses ; in 

 some instances, however, at a distance from the granite, altered 

 coarse ash puts on more the appearance of granite than does much 

 of the finer altered ash close to the granitic edge. 



While alluding to the oftentimes sharp line of division between the 

 purple, micaceous, and often porphyritic rock, and the true granite, 

 it is worth while to notice the patches of dark, fine-grained, and very 

 micaceous granite wbich frequently occur in the midst of the granite 

 of Shap. Such patches, having generally a more or less rounded 

 outline, seem to be very largely made up of small dark mica flakes 

 mingled with a less amount of quartz and felspar, the felspar very 

 seldom appearing in porphyritic crystals, as is so characteristic of 

 the granite in general. Now the line of junction between the 

 typical Shap granite and these highly micaceous dark patches is 

 quite as sharp as that between the granite and the general mass of 

 metamorphosed rocks around, and sometimes more so ; therefore it 

 would be unwise to say positively that the granite cannot be the 

 result of the extreme metamorphism of the ashy beds, because the 

 junction between the two is in many cases so definite. 



II. Microscopical Structure. 



A great many examples of these highly altered rocks having been 

 examined microscopically in thin slices, I will describe in general 

 terms the structure exhibited by specimens of the various lithological 

 stages already mentioned. The rocks showing the streaky lines 

 often curving round fragments of various sizes have been figured 

 and described in my previous paper before this Society*, and in the 

 Survey Memoir descriptive of the Keswick district ; therefore it is 

 sufficient to note the following facts regarding them, at the present 

 time. The positions from which the rocks referred to were obtained 

 are indicated in the sketch map (fig. 2, p. 592). 



1. First Stage. Felstone-like (and streaky) altered ash. — General 

 base often appears very fine-grained, and under crossed prisms is 

 dark, with minute points of light. On a close inspection of this 

 dark ground with a high power, it seems certain that the darkness 



* The Microscopic Eock-Structure of some Ancient and Modern Volcanic 

 Eocks. 



2r2 



