do PEOF. T. G. BON^'ET OX THE HUEONIAIf SERIES 



mineral have not a well-marked parallelism. This mineral is in 

 part of a pale olive or brovrnish-olive colour, in part colourless. The 

 latter is the ordinary white mica, giving bright tints with crossed 

 nicols ; the former is variably dichroic, giving onlj'^ low dull tints, 

 and is probably an altered brown mica. Distinct dichroism is 

 often exhibited as a cloudy spot in a flake, wheu the remainder is 

 feebly dichroic. This rock has some resemblance to one of the fine- 

 grained mica-schists, but it is by no means identical with them. 

 I have many typical specimens of the latter, such as occur in 

 Anglesey, in the upper group of schists in the Alps, &c., from all 

 of which this one differs, often very markedly. 



Macro scopically similar to the above, except that some light- 

 coloured specks are detected on close examination, are two speci- 

 mens sent by Dr. Selwyn, one labelled " Sudbury," the other " Be- 

 tween Sudbury and Vermillion river." Under the microscope, the 

 ground-mass is generally similar to the above, except, perhaps, that 

 there is not quite so much mica, and a larger proportion of it is the 

 colourless species. Many of the dark grains are rather prismatic in 

 form, and on applying a high power, appear to be a yellowish mineral, 

 blackened, often almost wholly, with opacite. The mica does not 

 exhibit any orientation. The spots are rudely rhomboidal in form, 

 and consist mainly of quartz granules with some mica, variable in 

 quantity, and rather irregular^ dispersed. The second specimen 

 has only varietal differences, but here there is a rather well-defined 

 border of white mica (chiefly) in the outer part of the rhomboidal 

 '• spot." The structure suggests that these may once have been sepa- 

 rate crystals, and I thinkit possible that the rock was either a volcanic 

 glass or tuffj containing crystals of felspar, in which both ground- 

 mass and crystals have subsequently undergone a rearrangement of 

 their constituents. 



(B) Proceeding next to the remarkable group of breccias (for the 

 fragments are more commonly angular than rounded) which occur 

 at intervals for certainly more than a mile along the railway west of 

 Sudbury, we find, as stated above, considerable variety in their 

 mineral character. It was impossible for me to bring away mate- 

 rials for an exhaustive study, so I secured a few of the more remark- 

 able specimens. The first, about half a mile from Sudbury, is a 

 compact grey rock, with pale-coloured spots of rather irregular form, 

 which weather to a pale cream-colour. In the field one could say 

 no more than that it might once have been a rather peculiar por- 

 phyritic trachyte, but that it rather resembled a true breccia, where 

 bits of a compact lava were imbedded in a somewhat quartzose, very 

 fine-grained matrix. Under the microscope it appears to be a 

 mosaic of irregular grains of quartz and felspar ; in what proportion 

 it is difficult to say, but the former certainly predominates, and in it 

 are scattered rather irregular fiakes of a brownish or greenish mica, 

 occasional larger grains, commonl}' associated, of quartz, and grains 

 of felspar with ragged outline, as if they had once been larger and 

 had been corroded by the matrix. Hence, even after microscopic 

 examination, one cannot venture to speak positively of the nature of 



