400 THE CRYSTAL FALLS IROif -BEARING DISTRICT. 



the recrystallizatioii, iu consequence of which the ordinary sedimentary 

 features that it originally possessed have been almost entirely obliterated. 

 Faint color banding, itself of secondary development, but no doubt pre- 

 serving a distinction in original composition, alone remains, and only here 

 and there, as a guide to the former stratification. By scattered indications 

 of this sort, and by the better evidence afforded by the overlying dolomite, 

 often very distinctly banded, it is known that the southern zone of 

 quartzite on the whole dips toward the north. Southward dips also occur in 

 this belt, by which it is known that subordinate folds occur within the quartz- 

 ite itself From the considerable variations in the surface width of the forma- 

 tion we are led to suspect the existence of more of these little folds than 

 we are able to prove. However, the secondary syncline, which extends 

 from the offset already referred to in sec. 35, T. 42 N., R. 30 W., for 6 miles 

 to the east to sec. 35, T. 42 N., R. 29 W., and includes no formation higher 

 than the quartzite, is very definitely determined. 



In the northern belt of the Sturgeon formation the indications of dip 

 are generally northward at very high angles. These indications, not in 

 themselves conclusive, are reenforced by a corresponding attitude in the 

 overlying dolomite, and it is therefore probable that there is a general, or at 

 least widespread, overturn in the dip of the northern belt. 



Since the contacts of the Sturgeon formation with the underlying 

 Archean and with the overlying dolomite are (except in one case) covered,' 

 it is impossible to obtain the data for very accurate determination of its 

 thickness. The uncertainty in most outcrops as to the dip of the quartzite 

 introduces an additional difficulty. However, in sec. 35, T. 42 N., R. 30 W., 

 on the west end of the range, and in sec. 33, T. 42 N., R. 28 W., 11 

 miles farther east, the covered intervals to the limiting formations are not 

 great, and if the contacts are not faulted (which is far from certain), the 

 minimum thickness is determinable within a reasonable limit of error. 



In the western locality the surface width of the zone probably under- . 

 lain by quartzite is about 500 feet. The quartzite itself is structureless, but 

 the overlying dolomite dips northward at an average angle of about 70°. 

 If the same dip holds in the quartzite, its true thickness is about 470 feet. 

 In the eastern locality similar data lead to a thickness of nearly 430 feet. 

 In these two sections the quartzite zone is much narrower than it is else- 

 where, either because undetected faults have reduced it, or because it is 



