THE SWAP GRANITE AND ASSOCIATED ROCKS. 285 



corner of the granite mass. Here a narrow band in the granite 

 consists mainly of pink felspar, but has some quartz intergrown 

 with it as a rude pegmatite [VD-t-TOn]. There is also mica with 

 the blade-like habit, as in the other case. The pegmatite band does 

 not border the granite, but runs horizontally at right angles to the 

 Tertical face of junction. 



A remarkable section is seen on the west side of Sherry Gill. 

 Here the granite is seen underlying the altered rocks with a low 

 angle of dip, and is probably a large sill rather than the main mass 

 of the intrusion. Along the junction runs what at first sight 

 appears to be a quartz-vein ; but on examination it is found that 

 the vein must have been a rather coarse-grained aggregate of felspar 

 and quartz (" pegmatite " of some writers), in which the felspar has 

 been largely replaced by quartz. The former mineral had often 

 crystal outlines, and the process of replacement, which began in the 

 interior of the crystal, is seen in various stages. A similar vein 

 cuts through this, as well as through the granite and the meta- 

 morphosed rock, proving that veins of this kind were not all pro- 

 duced simultaneously. 



As a somewhat analogous phenomenon may be mentioned a large 

 cavity seen in the heart of the granite-quarries. It occurs in con- 

 nexion with a joint, the surface of which is laid bare, and it has a 

 width of about six inches from the joint-surface. This is lined with 

 large felspars and quartz showing crystal faces, while around it is a 

 narrow margin of pegmatite with graphic structure. 



The geodes frequently contain well terminated crystals, and, in 

 addition to the minerals mentioned, we have noticed in these and 

 the joints talc, calcite, fluorite, malachite, iron pyrites, copper 

 pyrites, molybdenite, and mispickel (?). 



The replacement of the felspars by quartz at Sherry Gill, pre- 

 sumably an operation involving the agency of water, must belong 

 to a late stage in the history of the intrusion. Perhaps we may 

 assign to the same period the production of white mica along joint- 

 faces in the metamorphosed rocks, accompanied by modifications 

 extending to a very short distance from those planes. They have 

 been observed in the Andesitic Group near Wasdale Pike, in the 

 limestones of Wasdale Head Farm, and in the Coniston Flags of 

 AVasdale Beck. Mr. E. H. Acton has kindly examined spectro- 

 scopically the mica from the last locality, and finds in it no trace 

 of lithia ; it is apparently an ordinary potash-mica. 



§ III. The Dykes and Sills and their Relations to 

 THE Granite. 



An interesting group of intrusions is well exhibited in a valley 

 about a mile south of Shap "Wells Hotel at Stakeley Folds and Gill 

 Farm. Stakeley Folds is two thirds of a mile from the nearest 

 granite outcrop. Here, and within three or four hundred yards to 

 the south-east, four distinct sills are seen, injected one above the 

 other at slightly different horizons in the Coniston Grits. 



