2 J. CLIFTON WARD ON THE GRANITIC, GRANITOID, AND 



Introduction. 



The Skiddaw Granite occurs over several detached areas of small 

 extent in the mountain tract on the north side of Skiddaw and Blen- 

 cathra, much of which is known as Skiddaw Forest, the birth-place 

 of the river Caldew. The alteration in the surrounding Skiddaw 

 Slate extends in every direction for two or three miles from the cen- 

 tral mass, and is necessarily somewhat varied in character by the 

 changeable nature of the slate, which not unfrequently contains beds 

 of a sandy or even gritty texture. This last fact must be carefully 

 borne in mind when we consider the metamorphism which has been 

 effected. 



As in the last part of this memoir, the subject shall be dealt with 

 under the three heads of : — I. Examination in the field. II. Micro- 

 scopical Examination. III. Chemical Examination. 



In an Appendix short notices are given of similar researches on 

 these and kindred rocks. 



I. Examination in the Field. 



1. Unaltered Slate. — The general character of the unaltered clay- 

 slate is that of a bluish grey cleaved rock, seldom forming slates of 

 any value, but generally weathering into small flakes and chips or 

 into pencil-like fragments. The sand) r or gritty beds are usually 

 uncleared — but are very inconstant in character, and over the area in 

 question do not form beds of any thickness. 



2. First Stage of Alteration : Chiastolite Slate. — On approaching 

 the Skiddaw-granite area from the south, as on walking up the valley 

 between Skiddaw and Blencathra, the first trace of alteration met 

 with is the appearance of small faint spots on the cleaved surfaces of 

 the slate. These increase in number and size ; and many of them, 

 becoming more definite, assume the form of crystals of chiastolite, 

 which are soon found to traverse the slate in every direction, so that 

 very various sections of their rhombic form are displayed, frequently 

 showing a dark centre. The band of the chiastolite slate is seldom 

 more than a quarter of a mile in width. 



3. Second Stage of Alteration : Spotted Schist {Knotenschiefer). — 

 The slate just described passes gradually into a rock of a general 

 schistose character. It becomes more massive and less cleaved, the 

 planes of cleavage being replaced by those of an imperfect foliation, 

 which retain, however, the same general strike and dip, though they 

 are frequently contorted. 



The foliation seems to be due to the development of innumerable 

 little spots, mostly of a rectangular or oblong form, lying with their 

 longer axes in the planes of foliation ; and they give the rock a gene- 

 ral dark and spotted appearance. Large crystals of chiastolite and 

 andalusite* frequently traverse the mass; and in many parts minute 

 spangles of mica appear. 



* It will be borne in mind that chiastolite is but a variety of andalusite, and 

 the latter term may sometimes be nsed to include both. 



