Prof. T. G. Bonney — Foliation and Metamorpliism. 247 



convert what was once ordinary detritus into fine-grained mica 

 (mostly biotite) and quartz, probably authigenous, but as that 

 matrix becomes coarser, so the traces of a clastic origin grow more 

 distinct, till that becomes conspicuous in the breccias or con- 

 glomerates. I recognize in their fragments under the microscope the 

 following — granitoid rock (3 varieties), mica-schist (1), quartz-schist 

 (4), quartzite (2), ? halleflinta (2) ; still, even in these, mineral changes 

 appear to have occurred, some of which at least may be later in date 

 than the formation of the fragment. 



The cuttings on the Canadian Pacific Railway on both sides of 

 Sudbury Station exhibit similar cases of incomplete metamorphism. 1 

 Here we find two groups of rocks, one of which is more highly meta- 

 morphosed than the other, and is in much the same condition as that 

 at Obermittweida. The matrix is an aggregate of biotite and quartz 

 with some felspar. The first is mainly, the second to some extent, at 

 least, authigenous, the third probably clastic, though it may have 

 undergone subsequent augmentation. The larger fragments also 

 exhibit some changes, secondary quartz and white mica being 

 produced locally in the felspar, and the larger grains of quartz are 

 replaced by a mosaic of this mineral. Biotite occurs more sparingly, 

 in little flakelets, both clustered and isolated, which also suggests 

 a breaking up of original constituents of that mineral. Another group, 

 probably rather higher in position, occurs to the west of Sudbury, 

 which contains fragments of volcanic rocks and shows less signs of 

 metamorphism. There is also a group, traversed, as I was informed, 

 by the railway from Sudbury Station to Algoma Mills and Saulte 

 St. Marie, which seems to have been as much metamorphosed as the 

 Upper schists of the Alps. 2 The important fact, however, in the'two 

 groups mentioned above is that, while retaining indubitable traces 

 of clastic origin, they indicate very considerable mineral changes, 

 which, however, differ from those directly resulting from either 

 water, or pressure, or heat, when operating separately, though 

 probably demanding a rather considerable and prolonged action of the 

 last agent. 



We pass now to rocks, the origin of which is indubitable and the 

 metamorphism only micro-mineralogical. One instance will suffice, 

 because this exhibits the most marked departure from its original 

 condition, the group of the phyllites, a name often employed (as is 

 almost inevitable) rather vaguely, but which may be conveniently 

 restricted to argillaceous cleaved rocks, in which a minute secondary 

 mica has been developed in such large quantities as to constitute the 

 greatest part. These flakelets mostly lie in the same direction, 

 i.e. perpendicular to the direction of maximum pressure ; in fact, 

 a phyllite is the first marked step in the passage from a slate to 

 a schist. Phyllites occur in greatly folded districts, such as parts of 

 the Alps, Brittany, Scandinavia, Scotland, and Wales ; indeed, are 

 frequent in mountain regions, past or present. 



1 Locally these are broken into by moderately coarse syenites, sometimes 

 almost hornblende granites, and by basic rocks. 



2 A few specimens were shown to me at Sudbury. 



