478 MR. J. B. HILL ON PROGRESSIVE M.ETAMORPHISM [Aug. 1 899, 



brown mica, iron-ores entirely changed to leucoxene, large irregular 

 patches of felspar, epidote, green aggregates of chlorite, and very 

 long broken prisms of apatite. 



These epidiorites and hornblende-schists are clearly in- 

 trusive. They have a habit of occurring as sills, and it is not always 

 that good evidence of their intrusive nature can be obtained. In 

 the most unaltered areas, however, whenever a junction can be seen 

 between these epidiorites and the argillaceous or calcareous sedi- 

 ments, contact-alteration can be detected : the sediments near the 

 junction are intensely indurated, and will often no longer split along 

 their structural planes and joints. Argillaceous rocks are converted 

 into porcellanite, and limestones are often hardened. Besides this 

 induration, colour-banding has been set up in these argillaceous 

 or calcareous rocks, colours due to slight differences in composition 

 showing out far more prominently in the baked rock than in its 

 normal condition. JS'ear Kilchren an, where the sediments are least 

 altered, there is an example of a limestone, for 4 to 6 feet from its 

 junction with an epidiorite, having been converted into an epidosite. 



Besides the enormous amount of foliated igneous rocks now 

 represented by the hornblende- and chlorite-schists, intrusive 

 igneous rocks of post-schistose age are numerous over 

 the whole area. While the direct object of this paper would not 

 be furthered by a discussion of the interesting petrological phenomena 

 elucidated by a study of these various unfoliated intrusions and their 

 relationships one to another, a description of the area would neces- 

 sarily be incomplete that did not briefly refer to so dominant a 

 feature of its geology. 



In the northern part of the district we have the great protrusion 

 of Glen Fyne granite on the eastern flank, and the still larger 

 granite-mass of Ben Cruachan on the west. Between these two 

 masses we find smaller protrusions of granite, diorite, monzonite, 

 and rocks allied to hyperite, evidently related to these larger intru- 

 sions. In the north-eastern part of the area a numerous body of 

 sills occur on the eastern slopes of Upper Loch Pyne and of Glen 

 Eyne, and have their northern boundary very near the edge of the 

 Glen Fyne granite, with which they may probably have a relation. 

 They may be described generally as porphyrites, they vary in width 

 from a few feet to a dozen yards, and the group has a lineal ex- 

 tension of about 6 miles. 



Farther west, between Loch Fyne and the watershed between 

 that loch and Loch Awe, occurs a set of intrusions of a difterent 

 character. They run parallel with the strike of the strata, but 

 they may often have a width of over a mile, and one of these sills 

 extends over the entire length of the zone in which they occur, 

 having been traced for more than 15 miles. They are quartz- 

 porphyries of an unusual type, and are very closely related one 

 to another. Besides quartz, the felspar and biotite are also porphy- 

 ritic, and the rock is really a quartz-felspar-biotite-porphyry. The 

 biotite commonly occurs in stumpy prisms. 



