THE QUARTZITE TONGUE AT REPUBLIC, 

 MICHIGAN. 



I. 



On Major Brooks' geological and topographical map of 

 Republic Mountain and vicinity, Plate VI. of the Atlas of the 

 Geological Survey of Michigan, 1873, a tongue of the upper 

 quartzite (his formation, XIV.) is correctly represented as fork- 

 ing from the main mass of the same rock, and running northwest 

 along the top of the Republic bluff, a thin wedge of the under- 

 lying specular jasper (his formation, XIII.) being interposed 

 between them. 



No explanation of this singular occurrence was given by 

 Brooks in the text of the Michigan report. 



Dr. M. E. Wadsworth 1 in 1880, as the result of personal 

 examination, concluded that the supposed quartzite tongue was 

 reallv a granite dike, intruding the jasper. 



In consequence of later studies 2 by himself and his assistants, 

 Dr. Wadsworth has recently decided that his former determina- 

 tion of the tongue as a dike of granite was erroneous, and that 

 it is in fact quartzite. In this latest publication he endeavors to 

 explain the peculiar relations by the assumption that the inter- 

 posed wedge of specular jasper does not belong to the lower 

 series, but to the upper, and was deposited later than the 

 quartzite tongue. 



In the autumn of 1 891, in the course of extended work on 

 the surface and underground at Republic, I studied this question 

 in some detail, and concluded that the phenomena were due 

 entirely to faulting. 



1 Notes on the Geology of the Iron and Copper Districts of Lake Superior, 1880, 

 PP. 34-35- 



-Report of the Slate Board of Geological Survey, Lansing, 1893, pp. 129-130. 



680 



