Alfred Harker — Cordierite in the Lake-District. 169 



so characteristic of the Coal-measures, seem to have degenerated. 

 Many other Carboniferous insect relics are of great size, so that they 

 must have been dinosaurs of their kind, and the Neuroptera became 

 aldermanic and got fat and bulky on the well -grown and unctuous 

 Blatta. A plate of this fine insect, kindly presented to me by the 

 author, will appear in M. C. Brongniart's folio work on the Com- 

 mentry insecta, in due course. 



V. — Cordierite in the Lake District. 

 By Alfred Harker, M.A., F.G.S. 



TN the February Number of this Magazine, Mr. Hutchings 

 announces that he has identified as Cordierite the mineral 



which constitutes the conspicuous " spots " in the metamorphosed 

 slates of Wasdale Beck near the Shap Granite. In this connection, 

 it may be of interest to record another occurrence of the same 

 mineral, discovered by Mr. Marr and myself a year or two ago. It 

 is in the metamorphosed Skiddaw Slates of the Caldew Valley in 

 Cumberland, the locality of our specimens being south-west of the 

 farm of Swineside. The cordierite occurs there in crystals of quite 

 irregular shape, charged with various inclusions, original and 

 secondary, and stained with limonite. A transvei'se section is about 

 •07 or '08 inch in diameter, and shows the characteristic polysynthetio 

 twinning, causing a division into six sectors when viewed between 



Fig. Transverse Section of Cordierite Crystal in the metamorpliosed Skiddaw 

 Slates near Swineside, x 20 [slide 1563]. 



The drawing is in part diagrammatic, the division into six fields being, of course, 

 invisible in natural light. 



crossed nicols. In addition there is a division into an inner and 

 outer portion by a well-marked hexagonal zone of opaque, probably 

 carbonaceous, inclusions. The outline of the transverse section 

 itself shows only a general correspondence with the hexagonal 

 form, and extends as a ragged fringe into the surrounding part of 

 the rock. 



