ASSOCIATED METAMORPHIC ROCKS OP THE LAKE-DISTRICT. / 



account, it seems to me most reasonable to infer that the granite of 

 Skiddaw, which we see exposed at the surface, was not formed by 

 the extreme metamorphism of the rocks immediately surrounding it. 

 Had this been the case, there would probably have been a more 

 gradual passage, a transition from mica-schist into gneiss, and from 

 gneiss into granite, and the chemical composition of the junction 

 rocks would not have differed by so much as 22 per cent, of silica. 

 At the same time, as just now hinted, it is by no means improbable 

 that the granite was formed out of rocks of a similar class, at a 

 somewhat greater depth ; and the granite thus formed, and eating 

 its way upwards, would probably in great measure absorb into 

 itself the rocks immediately around. In connexion with this pro- 

 bable partially intrusive nature of the granite, the much- contorted 

 character of the mica-schist close around it may be noted. 



A further examination of the analyses shows that the last item 

 mentioned in each case represents both water and carbon, thus : — 



A 



Water 1-698 



Carbonaceous matter . . 2-035 



B 



C 



D 



1-298 



1-216 



0-397 



0-792 



0-717 



0-103 



3-733 2-090 1-933 0-500 



Wo have already seen that microscopical examination shows the 

 presence of carbon in considerable quantity in connexion with the 

 crystals of chiastolite ; and it decreases in amount through the 

 various terms of the series ; the same seems to be the case with the 

 proportion of water. 



It is interesting to note that the proportion of phosphoric acid 

 increases from A to D, just as, in Part II., we saw it increase among 

 the more highly altered members of the volcanic series, accompanied 

 by a decrease of carbonic acid ; but the percentage of phosphoric acid 

 in the specimens of slate analyzed (see also Part IV.) scarcely 

 seems to warrant the idea that what occurs among the volcanic 

 rocks was solely derived from these underlying slates. 



Summary. 



1. The spotted rock hitherto called hornblende slate, and well 

 developed in the tract known as Skiddaw Forest, may be con- 

 veniently termed spotted (or andalusite) schist (the indefinite 

 Knotenschiefer of the Germans). 



2. There is a complete passage in the field from unaltered clay- 

 slate, through chiastolite slate and spotted schist, to mica-schist. 



3. The junction between the mica- schist and the granite is well 

 defined, and there is no general transition from mica-schist into 

 gneiss (proper) and from gneiss into granite. 



4. Alteration of the clay slate begins by the formation of small 

 spots, which become developed into chiastolite and andalusite. 



5. The chiastolite slate passes into spotted schist by the great 

 increase of the small oblong or rectangular spots arranged along 



