684 THE JOURNAL OF GEOLOGY. 



base of the upper quartzite has been thrown, can be very 

 little greater than the thickness of that formation. Field study 

 shows clearly that the neutral surface of the folded material lay 

 below the base of the upper quartzite, and included a considerable 

 portion of the actinolite-schists. This is proved by the severely 

 contorted condition (showing compression) of the thinly bedded 

 jaspers, and by the same structure on a larger scale in the more 

 heavily bedded quartzite. The crowding of the rocks above the 

 neutral surface into a constricted space has resulted in the forma- 

 tion of three important synclines, separated by two anticlines, 

 all subordinate to the main fold. The most eastern of the syn- 

 clines occurs at the great open pit of the Republic mine ; the 

 middle, in the ground opened by the Morgan, Pascoe and Ely 

 shafts ; the westernmost in the neighborhood of the Swamp shaft 1 

 (Fig. i). These larger subordinate folds are accompanied by a 

 multitude of smaller anticlines and synclines, of various dimen- 

 sions. They are smaller, more numerous, and more closely 

 compressed in the iron-bearing member than in the overlying 

 quartzite. 



The upper quartzite, which is a massive and heavily bedded 

 rock, yielded to the compression by differential movements of 

 one bed over another, and doubtless also bv thickening. The 

 effects of the movement of bed on bed are strikingly shown at 

 numerous points in the horseshoe, perhaps particularly well in 

 the small open pit east of the Ely shaft. Here the individual 

 quartzite layers, from one foot upwards in thickness are separated 

 by parallel selvages of ground- up quartzitic material, varying in 

 thickness usually from two to four inches. In the case of one, 

 the measured thickness is eleven inches. These selvages, known 

 locally as a variety of " soap-rock," show frequently a vertical 

 pressure-cleavage. 



It is certain, then, that the original sheet of sediments, which 

 varied in character from thinly leaved jaspers - below to heavily 

 bedded quartzites above, and aggregated, for the area under dis 

 cussion, upwards of half a mile in thickness, has been bent back 



1 The Swamp shaft falls outside of the limits of Figure i. 



