. Bulletin of the Geological Society of America. Geology. LOCATION OF THE GLASS-BRECCIA. 139 ship it forms a sharp elbow apparently getting around an anticlinal axis and runs off to the eastward on the southern side of Vermilion lake ; but here, as above stated, it passes into a slaty conglomerate holding pebbles of syenite. In this form it is trace- able about ten miles more. "A good section of the typical form of the breccia may be seen in the cuttings near Onaping, where the Canadian Pacific railway intersects it, twenty-three miles north- west of Sudbury Junction. It has an average br
. Bulletin of the Geological Society of America. Geology. LOCATION OF THE GLASS-BRECCIA. 139 ship it forms a sharp elbow apparently getting around an anticlinal axis and runs off to the eastward on the southern side of Vermilion lake ; but here, as above stated, it passes into a slaty conglomerate holding pebbles of syenite. In this form it is trace- able about ten miles more. "A good section of the typical form of the breccia may be seen in the cuttings near Onaping, where the Canadian Pacific railway intersects it, twenty-three miles north- west of Sudbury Junction. It has an average breadth of fully a mile, and as it dips at angles of 45° and upwards it must have a thickness of over 4,000 feet. Owing to its hardness and toughness it has resisted denudation better than the sandstones and argillites, and it rises a few hundred feet above the latter in the form of a range of rugged hills overlooking the comparatively level country on the southeast. Along its northwestern side it is separated, in places at least, from the quartz-syenite by a massive band of ash-gray quartzite containing usually an abundance of white quartz pebbles scattered through it. " It was supposed that from its compact nature this breccia might be used in orna- mental construction ; but, while it gives a good, smooth surface, it has not been found susceptible of fine ; In a hand specimen this rock presents a nearly black felsitic matrix, in which are embedded sharply angular or slightly rounded fragments, vary- ing from li cm. in diameter downwards to ultra-microscopic dimensions. These fragments are lighter in color than the matrix, but differ considerably among themselves in their tint, structure and composition. The majority resemble chalcedony in appearance, others are greenish, while some of the largest fragments are now replaced by a single calcite individual. Occa- sional small grains of clear vitreous quartz may also be detected, while specks of magnetic pyrites (
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