CORDIERITE IN THE METAMORPHOSED 

 SKIDDAW SLATES. 



ALFRED HARKER, F.R.S. 



It is a reproach to Eng-lish petrolog-ists that no systematic study 

 has yet been made of the metamorphosed Skiddaw Slates of 

 Cumberland. Owing- to the underlying situation of the Skiddaw 

 granite," the aureole of metamorphism occupies a considerable 

 area, and different members of the Skiddaw Slate series are 

 involved in it. The different types of arg-illaceous and g-ritty 

 sediments, subjected to metamorphism in varying- deg-ree, have 

 g-iven rise to an interesting- variety of secondary minerals, which 

 have hitherto received but little notice. Clifton Wardf re- 

 cog"nised three chief types among- the metamorphosed slates, 

 representing- three successive stag-es of alteration : (i) Chiasto- 

 lite-slate, (2) Spotted- (or Andalusite-) schist, (3) Mica-schist. 

 Ward's work was done at a time when microscopical methods 

 in petrolog-y were still something- of a novelty, and his account 

 is not only very brief and partial, but is in some respects 

 incorrect. Certain errors were pointed out by Rosenbusch, j^ 

 who, however, knew the rocks onl}' from a few specimens. 

 Since that time practically no further information has been 

 published, except that in 1894, the present writer j noted the 

 occurrence of cordierite in some of the metamorphosed slates. 



The object of the present note is to draw the attention of 

 north-country petrolog-ists to a neg-lected field. The only new 

 fact to be recorded is that cordierite, formerly described from a 

 single locality, has a very wide distribution in the district, and 

 indeed is probably more abundant than andalusite. The two 

 minerals (including chiastolite as a variety of andalusite) are 

 often found together ; and in general one or other of them 

 predominates, or occurs exclusively, according to the com- 



* The several outcrops, in Sinen Gill, the Caldew V'alle}", and Grainsgill, 

 aie probably parts of one extensive mass, which is mostly concealed. See 

 Quart. Journ. Geol. Soc, vol. li. (1895) p. 140. 



t Quart Journ. Geol. Soc, vol. xxxi. (1875), pp. 568-602 ; vol. xxxii (1876), 

 pp. 1-34. The Geology of the Xorthern Part of English Lake District, Mem. 

 Geol. Sur. (1876), pp. 9-12. 



X Die Sfciger Schiefer, Geol. Sur. Alsace-Lorraine (1877), pp. 211-213. 

 .\ translation is gfiven in A'aturalist, 1892, pp. 119, 120. 



i5 Geol. Mag. 1894, PP- '69, 170. 



1906 April I. 



