Page:The Journal of geology (IA journalofgeology21894univers).pdf/470

Van Hise^[1] describes the Huronian volcanics south of Lake Superior. These include both lavas and tufas interstratified with each other and with contemporaneous clastics. Among the lavas are amygdaloids, the amygdules of which are in certain cases jasper similar to that of the iron formation adjacent, and believed to have been formed at the same jasper forming period. The volcanics are much more altered than those of the Keweenawan. They are found in various places, but the most extensive areas are in the Gogebic district west of Gogebic lake, and in the Michigamme district north of Crystal Falls. In the first locality the series is 7,000 or 8,000 feet in thickness. This great mass of material was piled up, while to the west 700 to 800 feet of the sediments of the iron-bearing formation were accumulating. In this district, therefore, at the same time there was being deposited the ordinary sediments of the area and locally a volcanic series of a wholly different character.

^[2]Bayley describes actinolite-magnetite-schist from the Mesabé range of Minnesota. This rock differs from the corresponding schists of the Penokee series only in that quartz is rare and hematite is absent.