RESEARCHES IN THERMAL METAMORPHISM. 299 



enclosed fragments were originally of granite. The ferro- 

 magnesian minerals of this rock, mica and hornblende, 

 have been dissolved and absorbed by the diabase magma, 

 rarely leaving any trace. The felspar crystals, chiefly 

 microcline, have been attacked at the edges and penetrated 

 along countless small cracks, which gave the basic magma 

 access to the interior, where hollows have been dissolved 

 out. The quartz grains of the granite have been only ex- 

 ternally corroded and are thus rounded. The magma has 

 given rise within and around the old microcline crystals to 

 prisms of an intermediate soda-lime-felspar, in parts inter- 

 grown with quartz, and the effects produced may be likened 

 in some respects to those described in the large felspar 

 crystals of the Shap granite where they are enclosed in the 

 dark and relatively basic portions of that rock (3). 



The permeation or injection of a rock by an igneous 

 magma, which we are here asked to consider, is clearly 

 something more than mere thermal metamorphism, and 

 must be essentially a contact action. It seems doubtful 

 whether it has operated, except on a very restricted scale, 

 at any ordinary junction of a metamorphosed rock with an 

 intruded magma. Sollas has described it at the contact of a 

 gabbro with a later intrusion of granophyre in the Carling- 

 ford district (30). The latter rock has penetrated the 

 former in dykes and veins of all gradations of size down to 

 microscopic films and specks occupying minute cracks and 

 cavities in the gabbro, and the author seems to be of 

 opinion that quartz-bearing gabbros in general have origi- 

 nated in a similar fashion. At Carrock Fell, however, 

 where somewhat similar relations have been investigated 

 by the present writer, such a process of injection seems to 

 have been confined to a very narrow zone along the actual 

 junction of the gabbro and granophyre, while the main body 

 of quartz-gabbro owes its origin to a special kind of differ- 

 entiation in the gabbro magma while still fluid (20). In the 

 Irish case the details given of the extent and mode of occur- 

 rence of the rock types described are scarcely enough to 

 warrant any expression of opinion on this point. Sollas 

 has also described, in County Wicklow, the transformation 



