OUTLINE OF THIS MONOGRAPH. 



The Maniuette district occupies an area extending from Mariiuotte on Lake Superior west to 

 Michigamnie, a distance of something less than 40 miles. The breadth of the area of the Marquette 

 series proper varies from about 1 mile to more than 6 miles. From the western part of the main area 

 two arms project for several miles, one to the southeast, the Republic trough, and one to the south, 

 the Western trough. 



The rocks in the district comprise three series, separated liy unconformities. These are the 

 Basement Complex or Archean, the Lower Marquette, and the Upper Marquette, the two latter 

 constituting the Algonkian for this district. The Basement Complex gives no evidence of water 

 deposition. The Lower Marciuette and Upper Marquette series are mainly sedimentary, although 

 large masses of igneous rocks are included. Each of the series of the district consists of several 

 formations. The transgression of the Lower. Marquette sea took place slowly, so that in parts of the 

 district the Lower Marquette succession is incomplete. lu other parts the succession is incomplete 

 because of inter-Marqnette erosion. .Vfter the Upper Marquette series was deposited the district was 

 folded, ftiulted, and fractured in a complex fashion, with resultant jirofound metamorphism. 



Chapter I gives a history of geological explorations in the Manjuette district, and a full summary 

 of previous literature. 



Chapter II treats of the Basement Complex. This occurs in two main areas, one north of the 

 Marquette series, called the Northern Complex, and one south of the Marcjuette series, called 

 the Southern Complex. There are also isolated areas within the Algonkiau. The Basement Complex 

 is composed of schistose and massive phases of crystalline and jiyroclastic rocks, so different from the 

 Algonkian sediments that there is rarely any difficulty in distinguishing between them. The schistose 

 phases are acid, intermediate, and basic. They are cut by a variety of massive igneous rooks, basic, 

 acid, and intermediate, in the forms of bosses and dikes. The rocks are undoubtedly of widely 

 different ages, but we are unable to separate them into sharply defined series upon the basis of age. 



The Northern Complex is treated under the divisions Jlona schists, Kitchi schists, gneissoid 

 granites, hornblende-syenites, basic dikes, acid dikes, pcridotite, and ferruginous veins. The Mona 

 and Kitchi rocks are greenstone schists, which are believed to be largely reorystallized volcanic 

 materials. Their original forms included both tuffs and lavas. Basic schists are ]>redominaut, but 

 acid schists are found. The Mona schists are noncouglomeratic green schists. The Kitchi schists 

 contain numerous pebble-like bodies, which give them in many places a conglomeratic appearance. 

 The gneissoid granites and syenites are plutonic intrusive rocks within the greenstone schists. The 

 basic dikes are mainly diabase. The majority of these are schistose, and earlier than the upper beds 

 of the Marquette series. A few are fiesb, and these are probably of Keweenawan age. The peridotite 

 is older than the Cambrian sandstone, and younger than the greenstone schists of the Basement 

 Complex. The ferruginous veins are believed to be water-deposited, and were formed previous to 

 the deposiMan of the Lower Marquette series. 



