XXVI OUTLINE OF THIS MOXOGRAPH. 



which quickly passes upward into a qiiartzite. As the sea occupied a considerable time in advancing 

 over the land area, and as the advance was from the east, several formations were deposited in the 

 eastern part of the district before the entire area was submerged. These formntions are the Mesuard 

 qnartzite, the Kona dolomite, and the Wewe slate. Thus we have these formations and the overlying 

 Ajibik quartzite overlapping one another to the west. It follows that the transgression horizon is 

 somewhat arbitrarily divided between four formations. 



The Lower Marquette series rests unconformably upon the Archean. This is shown at many 

 localities by numerous unconformable contacts and great basal conglomerates, the main part of 

 the detritus being in each case identical with the rocks of the Basement Complex at that locality. 

 Within the sediments of the Lower Marquette series are a few thin lava beds, showing volcanic 

 activity in Lower Marquette time. After the deposition of the Lower Marquette series the land was 

 raised above the sea, and erosion set in and continued for a long time. The denudation was deep 

 enough in some places to remove the entire Lower Marquette series. The Upper Marquette series was 

 therefore deposited unconformably upon the Lower Marquette series and the Archean. For the major 

 part of the district the immediately subjacent rocks belong to the Negauneee formation, and the basal 

 conglomerate for this area consists mainly of detritus derived from that formation. For smaller 

 areas other formations of the Lower Marquette series or the rocks of the Basement Complex underlie 

 the Upper Marquette rocks, in which cases the detritus is derived mainly from them. Above the 

 conglomerate, the first deposit of the advancing Upper Marquette sea, a sandstone was piled up, 

 which was later transformed to the Goodrich quartzite. In the western part of the district, above 

 this came a sideritic slate, which has been changed to a griinerite-magnetite-schist — the Bijiki schist. 

 Above the Bijiki schist followed the muds and volcanics which have been transformed respectively to 

 the rocks of the Michigamme and Clarksburg formations. Within the Lower and I'pper Marquette 

 series are abundant intrusives. 



After the deposition of the Upper Marquette series the three series of the district were folded 

 together. The folding is of a complex character. The largest but least conspicuous folds have an 

 east-west direction. The miijor east-west fold is a great synclinorium, which in the central part of 

 the area is of the abnormal type. Upon the primary folds are secondary ones, upon these tertiary ones, 

 and 80 on to microscopic plications in the case of the finer-grained rocks. The more plastic forma- 

 tions vielded mainly by do wage ; the less plastic formations yielded partly by fracturing, although in a 

 large way obeying the general folding of the district. At many places the fracturing was so complete 

 as to produce reibungsbreccias, or even pseudo-conglomerates. A microscopical study shows that not 

 a cubic inch of material has escaped dynamic action. Every original grain of fair size gives evidence 

 of interior movement. The rocks have been kneaded throughout. As a result of the dynamic action, 

 there has also been faulting, but with two or three exceptions the faults are so small as to be unim- 

 portant. The manner in which the rocks have responded to deformation shows that when folded they 

 were in the zone of combined fracture and flowage. It is believed that they were buried under a 

 thickness of several thousand feet of sediments, perhaps as much as 10,000 feet. 



The various formations of the Marquette series, as a result of the dynamic and other processes, 

 were metamorphosed in different ways, dependent upon their composition and position. In the softer 

 rocks cleavage and tissility were generally developed, and the rocks were extensively transformed to 

 slates or schists. In the harder rocks these structures are less prevalent, although at many places 

 alon" the major planes of accommodation, and especially at the contacts between the Basement Com- 

 plex or Archean and the Marquette series between the Lower Marquette and Upper Marquette series, 

 they also have beeu transformed into crystalline schists. At the former place the Archean rocks have 

 been transformed into similar crystalline schists. The rocks upon opposite sides of a contact have par- 

 allel schistosity, and therefore there are here apparent gradations between the unconformable Lower 



