﻿Vol. 66. ,] SKIDDAW GRANITE AND ITS METAMOEPHISM. 125 



Clifton Ward recognized three zones, and summarized the results 

 of his observations as follows : 



' On approaching the altered area, the slate first becomes faintly spotty, the 

 spots being of a somewhat oblong or oval form, and a few crystals of chiasto- 

 lite appear. Then these crystals become more numerous, so as to entitle the 

 rock to the name of Chiastolite Slate. This passes into a harder, more thickly 

 bedded, foliated and massive rock, Spotted (or Andalusite) Schist; and this 

 again into Mica Schist of a generally grey or brown colour, and occurring 

 immediately around the granite.' (Op. cit. p. 9.) 



Rosenbusch, in his classical memoir on the Steiger Schiefer, 

 criticizes this statement, and states that from his own observations 

 the development of chiastolite here as elsewhere precedes the 

 formation of spots : hence chiastolite-slate must be regarded as the 

 •equivalent of spotted clay-slate (Knotenthonschiefer), and this is 

 succeeded by spotted mica-slate (Knotenglimmerschiefer). 



Prom a careful study of the literature, as well as from my own 

 observations, it appears that these two writers were not referring 

 to the same thing, hence the misunderstanding. There are, in point 

 of fact, two spotted zones : the first or outer spotted zone is not 

 everywhere developed, but occurs in several places, as, for example, 

 the western face of Skiddaw, outside of the chiastolite zone. This 

 is the type referred to by Ward in the first sentence of the extract 

 just quoted. The inner spotted zone is the Knotenglimmerschiefer 

 of Rosenbusch, and in this zone, as was pointed out by Harker, 1 

 the spots consist of cordierite; this is also the spotted (or andalu- 

 site) schist of Ward. Rosenbuseh appears to ignore altogether the 

 highly micaceous facies, which is not noticeably spotty. 



Ward's description, therefore, with some modifications, may be 

 regarded as substantially correct with reference to the sequence of 

 rock-types as seen in the Glenderaterra valley ; but it does not take 

 into account the great variations of lithological type in the unaltered 

 and altered rocks in other parts of the area. As will be shown in 

 detail in the following pages, these originally different rock-types 

 give rise to metamorphic rocks showing also a considerable amount 

 ■of variation. 



It is obviously impossible to give a detailed description of all the 

 varieties of altered rock, which are endless in number and shade 

 indefinitely into one another. However, as has been before stated, 

 three fairly well-marked types are involved in the aureole : namely, 

 black slate, grey flaggy slate, and rather massive grit. The effects 

 of metamorphism on each of these will be considered separately as 

 a matter of convenience, taking them in the following order : — 



(1) The soft black slates of the Glenderaterra district on the south, and 



Dead Crags, near Dash, on the north. 



(2) The grey flaggy bands which succeed these slates on the north and 



south respectively. 



(3) The central grit-band of the Caldew valley. 



This order is probably the inverse of the stratigraphical age, and 

 is adopted merely as a matter of geographical convenience. 



1 ' The Naturalist ' Leeds, 1906, p. 121. 



