ANALYTICAL ABSTRACTS. 447 



of several geologists as to the descending succession of the rocks of North- 

 eastern 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 frag- 

 mentals 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 magnet- 

 ite, are associated with contemporaneous felsites, quartz-porphyries and red 

 granites. This gabbro includes several masses of the next older strata, par- 

 ticularly the Pewabicquartzite. 



4. The Animikie. This series is characterized by a great quartzite associ- 

 ated with the iron ores and cherts. The quartzite (Pewabic) lies unconform- 

 ably on all the older rocks. It often is conglomeratic, bearing debris of the 

 underlying formations. Within it is mingled volcanic tuffs from contempora- 

 neous eruptions. The Pewabic quartzite includes that of Pokegama Falls 

 on the Mississippi River, and of Pipestone County. In the vicinity of con- 

 temporaneous volcanic disturbances its grain is fine, like jaspilite, and some- 

 times it has acquired a dense crystalline structure from contact with the 

 gabbro. 



5. The Keewatin. This is a volcanic series of great thickness, being com- 

 posed 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 strati- 

 form, 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 uncer- 

 tain 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 



