THE HEMLOCK FORMATION. 441 



of the center of sec. 16, T. 45 N., R. 31, a few exposures occur, the struc- 

 tiu'e of which strikes a few degrees west of north and dips eastward at 

 angles of 45° to 50°. In sections 21 and 28, a mile and a half south, numer- 

 ous outcrops in similar attitudes are found along the northern river section. 

 In sees. 3 and 4, T. 44 N., R. 31 W., a few scattered outcrops only have 

 been found, but throughout section 10 they are very abundant. For the 

 next 2 miles south through sees. 15 and 22, T. 44 N., R. 31 W., only a 

 few small exposures have been discovered which have the same northerly 

 strike and eastward dip. Thus for a distance of 11 miles along the strike 

 exposures occur at comparatively short intervals, the longest gap being 3 

 miles. 



In general this belt is one of slight elevation above both the dolomite 

 country on the west and the iron formation country on the east. The areas 

 of best exposure are characterized by very rough topographical details, 

 which are entirely lost in the generalized curves of the map. Abrupt strike 

 ridges, separated by narrow ravines, succeed one another at short intervals. 

 In the covered areas the surface, while retaining its general elevation, has 

 been leveled off by the deposition of till in the hollows, and has the smoothly 

 undulating contours characteristic of till-covered areas. 



FOLDING AND THICKNESS. 



No secondary folds have been detected within the Fence River area of 

 the Hemlock formation, and on account of the metamorphism and cleavage 

 structural observations are not possible from which they might be inferred. 

 The only clear evidence as to the attitude of the rocks was afforded by the 

 contact at one locality between beds of amygdaloid and agglomerate. 

 There the dip is. eastward at an angle of 50°. The surface width of the 

 formation vai'ies between 2,000 and 3,000 feet. If 50° is taken as the dip, 

 the thickness would be from 1,500 to 2,300 feet. If the average dip is 

 assumed to be 40°, or the average of the observed dips of the underlying 

 dolomite, the thickness would be from 1,300 to 1,900 feet. Or if 30° b© 

 taken, the average of the lower dips of the dolomite, the thickness would 

 be 1,000 to 1,500 feet. We may say, therefore, that the thickness north 

 of the southern river section is probably not less than 1,000 nor probably 

 more than 2,300 feet. South of the southern river section the thickness 

 diminishes rapidly. 



