IN THE NEIGHBOURHOOD OP SUDBURY, CANADA. 41 



istic andesitc, the others, more compact, are probably the same species ^ 

 these are perhaps even better preserved than the fragments in the vol- 

 canic grits of Charnwood Forest. "With them are two fragments of 

 a granitoid rock, one of which has its quartz in compound streaks, 

 i. e. exhibits a gneissic structure, probably the result of pressure, but 

 anterior to the detachment of the fragment. Another (from the east 

 end of the same island) consists of rather similar materials, but the 

 volcanic rock is more basic, containing a considerable amount of viri- 

 dite and chlorite, and the granitoid fragments (the commoner) 

 indicate very curiously the results of fracture, under pressure, and 

 recementation. A third (between Upper and Lower Rapids, Yer- 

 million lliver, C.P.R.) consists of rather angular fragments of quartz 

 and felspar, and of flakes of altered brown mica, evidently the 

 detritus of an old granitoid rock, where the proportion of the mate- 

 rials has not been very much changed by drifting. Another (be- 

 tween Spanish and Sable Rivers, C.P.R.) has an argillaceous matrix, 

 with a few scattered grains of quartz, but contains a comparatively 

 large fragment of a rock which has the structure of a true granite 

 rather than a gneiss. The last (Campment d'Ours*) is crowded 

 with fragments, andesite or porphyrite (4 varieties), granitoid rock, 

 and a fine-grained gneiss, with marked foliation. The matrix also 

 is obviously the detritus of the above materials, chiefly of the second. 

 That rock, it may be remarked, contains much microcline, and ex- 

 hibits a structure characteristic of the granitoid gneisses so common 

 in the lower part of the Laurentian series. 



(2) The next group has undergone changes like and about equal 

 to those described in the Sudbury district. White quartzites, from 

 between Serpent River and Algoma Mills, i. e. about 8 miles from 

 Lake Huron, on a line branching from Sudbury, and from between 

 Sable and Spanish Rivers, C.P.R. f These have clear quartz grains 

 imbedded in a colourless micaceous " paste," in which is sometimes 

 a darker mica and iron-oxide. This is more abundant in the second 

 (darker) specimen. 



Lastly is a very interesting rock. The ground-mass consists of 

 micas, greenish and colourless, in well-defined flakes from about 

 •002" to -004" long, associated rather irregularly with granules of 

 clear quartz, generally of less diameter, and some grains o£ opacite^ 

 in which occur somewhat oblong spots consisting chiefly of white 

 mica and granular quartz, the mica being to a large extent collected 

 about the edges. I suspect that this rock was once a microporphy- 

 ritic igneous rock, probably an andesite or quartzless trachyte, sub- 

 sequently changed. 



With these rocks may be included a grey limestone (from Echo 

 Lake, some distance east of Sault Ste. Marie), the outside of which 

 is weathered very curiously into a sort of ridge and furrow t^ 



* An island at the east end of the narrow channel between Lake Greorge and 

 North Channel on Lake Huron. 



t These, according to Logan, come well above the great conglomerates. So 

 also does the well-known " red-jasper conglomerate." 



I Undoubtedly No. 5 in the series given by Logan, p. 56. Here, as in 

 another place, it divides an upper from a lower mass of conglomerates. Here 

 a thickness of 300 feet is assigned to it. 



