Page:The Journal of geology (IA journalofgeology11893univers).pdf/114
them both on a large and small scale, that it was impossible to separate them. Within the Huronian trough, and parallel with it, is also a tongue of gneiss and hornblende-granite two or three miles wide and thirty-nine miles long.
The Huronian division forms a part of the great Huronian belt, extending from Lake Superior and Lake Huron nearly to Lake Mittassini. The bedding of the Huronian is usually nearly vertical, or stands at high angles. Occasionally the rocks have been sheared by pressure. Graywacke-conglomerate, in places full of rounded pebbles of gray quartz-syenite, is found on the Blue River branch of the Spanish River, Lot 2, Con. III. In the township of Hyman is an Augen-gneiss which is evidently a metamorphorsed clastic, as it forms a part of the quartzite and graywacke series. The line of junction between the Laurentian and Huronian is unusually straight. West of Lake Wahnapitae, along the contact, there is evidence of great disturbance and crushing, the rocks of the two series being much broken up and intermixed. It is not improbable that at the junction line is a considerable fault.
The third division is less altered, and is in a distinct basin running from the township of Trill northeastward to near the South Bay of Lake Wahnapitae, a distance of 36 miles, with a breadth of 8 miles in its central portion. These rocks are perhaps unconformable to the older Huronian rocks on which they rest, and may be Upper Huronian, or possibly lower Cambrian.
Along Onaping Lake and River, and along Straight Lake, are Huronian outliers. The principal kinds of rocks in the first basin are slate conglomerates, with well-rounded pebbles and boulders, mostly of binary granite, quartz, quartzite and schists; and coarse arenaceous or graywacke conglomerate, together with some pale-pink quartzites and blueish and greenish-gray felsites, argillites and slates. The principal rocks of the second basin are graywacke-schists, quartzites, quartzite or graywacke-conglomerates, green schists, hard sandstones, greenstones, and some dolomites. In the conglomerates are pebbles of graywacke and hornblende-granites like the prevailing varieties found in situ in the region, black slates and black and white quartz. On Lot 4, Con. III, Moncrieff, is the junction of the Laurentian red hornblende-granite and the graywacke.
It is concluded that the Huronian rocks of the Sudbury district are largely of volcanic nature, although many of them have been rearranged by water; hence they may be termed pyroclastic. The graywackes consist of granite debris more or less comminuted by the modifying action of water. Under this name is included many varieties of rocks, ranging from those which approach quartzites to others approaching argillites. The largest fragments are usually of red or gray aplite. As a general rule, the different divisions of the Huronian rocks do not maintain their thickness very far on the strike, but diminish more or less rapidly, their place at the same time being filled by a corresponding thickening of other members of the series.