OUTLINE OF THIS MONOGRAPH. 



Chapter I. The Crystal Falls district is situated on the Upper Peninsula of Michigan, and 

 forms a connecting link between the Marquette and Menominee districts of Michigan. A history of 

 the previous work in the district, accompanied by a summary of the literature, is given, and there is 

 reproduced a series of maps which indicate the development of knowledge concerning the disiribution 

 of the rocks and their structural relations. As explanatory of the locations given, the mode of work 

 is described and the object and method of taking magnetic observations is briefly outlined. 



Chapter II treats of the geographical limits, structure, stratigraphy, and physiography. The 

 portion of the district here described includes approximately 540 square miles. Structurally it is 

 closely related to the Marquette district ; the essential features being a northwest-southeast set of 

 folds, with a superimposed series trending northeast-southwest. The oldest rocks belong to the 

 Archean. They cover an oval area which is surrounded by the Algonkiau rocks represented by the 

 Lower and Upper Huronian series. The Archean and Algonkian are overlain with strong uncon- 

 formity by rocks of the Cambrian division of the Paleozoic. The drift deposits of the Quaternary 

 are everywhere present. Only the pre-Paleozoic rocks, however, are discussed. The most noticeable 

 topography is that of the drift, which in places is seen to be superimposed upon pre-Pleistocene 

 topography. The maximum elevation is 1,900 feet above sea level, and the minimum 1,250 feet. The 

 conclusion is reached that this portion of Michigan before Glacial times had been reduced to the 

 condition of an approximate peneplain. The drainage is chiefly by a few large streams which flow 

 into Green Bay of Lake Michigan. A small part is drained by streams flowing into Lake Superior. 

 In portions of the area the drainage has reached an advanced stage, in other portions it is very 

 youthful. The development of the drainage is illustrated in the case of the Deer River. The timber 

 and soil vary much in character. 



Chapter III treats of the Archean. The rocks of this age form an elliptical core, following the 

 axis of a northwest-southeast trending anticline. Exposures are few because of the superimposed 

 drift. The Archean is overlain unconformably by Algonkian sediments derived from the granite, and 

 there is absence of contact action. These facts indicate that it was the floor upon which the over- 

 lying sediments were deposited. Petrographically it consists chiefly of biotite-grauite. On the 

 periphery of the area a biotite gneissoid granite is very well developed. Some of this at least is 

 of dynamic origin. The Archean is cut by acid and basic dikes which are now both schistose and 

 massive. 



Chapter IV treats of the Lower Huronian series. This series is subdivided into the following 

 formations, from the base upward : The Randville dolomite, the Mansfield slate, and the Hemlock 

 volcanics. 



Section I. The Randville dolomite is poorly exposed. It consists of quartzose dolomite, grading 

 down into quartz-schist and recomposed granite. It has evidently been derived partly from the 

 granite, and is considerably younger than that. Its relations to the overlying formations were not 

 observed. The thickness could not here be determined, but, in the area studied by Smyth, its maxi- 

 mum is about 1,500 feet. 



