Page:The Journal of geology (IA journalofgeology21894univers).pdf/463

of several geologists as to the descending succession of the rocks of Northeastern Minnesota.

1. Keweenawan or Nipigon series unconformably beneath rocks bearing the "Dikellocephalus" fauna, and consisting of fragmental and eruptive beds, the upper portions being almost entirely red sandstones.
2. Alternating beds of eruptive sheets and fragmental rocks. The fragmentals are thin bedded slates, actinolite-schists, magnetitic jaspers, cherts and quartzites. The sheets are ordinary eruptives or pyroclastics.
3. Immense quantities of true gabbro often bearing Titaniferous magnetite, are associated with contemporaneous felsites, quartz-porphyries and red granites. This gabbro includes several masses of the next older strata, particularly the Pewabic quartzite.
4. The Animikie. This series is characterized by a great quartzite associated with the iron ores and cherts. The quartzite (Pewabic) lies unconformably on all the older rocks. It often is conglomeratic, bearing debris of the underlying formations. Within it is mingled volcanic tuffs from contemporaneous eruptions. The Pewabic quartzite includes that of Pokegama Falls on the Mississippi River, and of Pipestone County. In the vicinity of contemporaneous volcanic disturbances its grain is fine, like jaspilite, and sometimes it has acquired a dense crystalline structure from contact with the gabbro.
5. The Keewatin. This is a volcanic series of great thickness, being composed mainly of volcanic tuffs, presenting more or less evidence of aqueous sedimentation, but conglomerates, graywackes, quartzitic schists, and glossy serpentinous schists are present. The Kawishiwin formation, apparently the upper member of the series, embraces the great bulk of the greenstones, chloritic schists, jaspers, and hematites. The iron ores are in lenticular lodes, and stand upright conformable with the general position of the rocks.
6. The Keewatin series becomes more crystalline towards the bottom, and passes conformably into completely crystalline mica-schists and hornblende-schists, which are named the Vermilion series. The rocks are usually stratiform, contain magnetic iron ore, and embrace some dark massive greenstone belts, in which no stratification bands are visible.
7. The Laurentian. When not disturbed by upheaval the Vermilion schists pass into Laurentian gneiss, there being a gradual increase in the feldspathic and siliceous ingredients. Even after the Laurentian characters are apparently fully established, conformable bands of Vermilion schists reappear: from which it is plain that the base of the Vermilion is an uncertain plane, which can not be located exactly. This normal passage from the Vermilion to the Laurentian is frequently disturbed by the intrusion of numerous dikes of light colored granitic and basic rocks. These were both in a fluid state, the only non-fluid rocks being the schists which are embraced