LNTRODUCTION. 331 



plexity of the area, it is very probable that further study of important local- 

 ities would clear away many of the difficulties, as well as modify certain of 

 the opinions now held. 



The writer was efficiently aided in the field work by Messrs. Samuel 

 Sanford and Charles N. Fairchild for nearly the whole period, and E. B. 

 Mathews and H. F. Phillips for part of it, as assistant geologists, and by 

 Messrs. Lewis and Forbes as skilled woodsmen. 



PRELIMINARY SKETCH OF THE GEOLOGY. 



The rocks of the Michigamme and Felch Mountain areas range in age 

 from Archean to early Paleozoic. North and west of the Michigamme 

 River, where geological boundaries are most susceptible of determination, 

 the granites and gneisses of the Archean come to the surface in three oval 

 areas of great regularity of outline, from 10 to 12 miles long by 2 to 6 

 miles wide, while the intervals between the Archean ovals are occupied 

 by highly tilted sedimentary and igneous rocks of Algonkian age. The 

 lower member of the Algonkian has derived its materials from the wasting 

 of rocks lithologically similar to the underlying granites and gneisses. In 

 the southern and eastern portions of the district the edges of the tilted 

 older rocks are partially covered by a blanket of gently dipping sandstones 

 of Cambrian age, very soft and easil}" disintegrating. These rocks first 

 appear near the Michigamme River as detached outliers. In going south 

 and east from that river the separated patches become larger and more 

 abundant, until finally a few miles beyond the eastern limit of our work in 

 the Felch Mountain range they unite and entirely cover the pre-Cambrian 

 formations. 



CHARACTER OF THE SURFACE. 



In its most general asjsect the surface throughout this area is a plaui, 

 somewhat rolling indeed, which slopes gently upward from the southeast 

 toward the northwest. The surface is formed partly by the soft and gently 

 inclined Upper Cambrian sandstones and partly by the much harder and 

 highly tilted pre-Cambrian rocks of diverse physical and mineralogical 

 characters, and yet over all it maintains a very uniform slope. On the 

 southeast, in the Felch Mountain range, the plain has an average elevation 

 above the sea of 1,200 to 1,300 feet. In the northwest, in the southern 



