SECONDARY STRUCTURES OF BARABOO QUARTZITE 263 



fissures. On the South Range, the majority of these independent 

 joints, about 60 per cent, of the total number of joints, strike N. 60 E. 

 and N. 30 W. Nearly 20 per cent, strike N. 20-30 W., and the 

 remainder strike in various other directions of the compass. On 

 the North Range, the principal directions of rupture independent of 

 the fold are N. 30-40 E., and N. 30-40 W., and N.-S. 



It has been found that some of the joints unrelated to the folding 

 are connected with deformation of the Cambrian. Thus the pre- 

 dominant directions of jointing in the Cambrian of the eastern end 

 of the quartzite range is N. 60 E. and N. 30 W., which is the pre- 

 dominant direction of rupture of the quartzite on the South Range. 

 This does not preclude the possibility that this set of fissures existed 

 in the quartzite before the deformation of the Cambrian. It has 

 been observed repeatedly that N. 60 E., N. 30 W., N. 10 E., N. 30 E., 

 N. 35 E., N. 50 E., N. 20 W., N. 25 W., N. 35 W., N. 60 W., N. 70 W., 

 N.' 80 W. joints are continuous through both Cambrian sandstone 

 and pre-Cambrian quartzite. On the other hand there is abundant 

 evidence that many joints independent of the fold existed in the 

 quartzite before the Cambrian was deposited, since (i) these con- 

 tinuous vertical joints are more prominent in the quartzite than in 

 the- Cambrian; (2) the quartzite conglomerate bowlders at the base 

 of the Cambrian are dissected by a diversity of joints, some of 

 them cemented with quartz, many of which could not have been 

 related to the folding, or have developed by processes connected 

 either with the deposition or the deformation of the Cambrian; (3) 

 the Cambrian sandstone has been deposited in wide gaping fissures 

 of the quartzite whose directions are independent of dip and strike 

 relations of the quartzite. Thus at Devil's Lake where the quartzite 

 strikes N. 65-75 E., and dips from 5-25 N., a vertical fissure several 

 feet in width, striking N. 25 W., is filled with Cambrian sandstone. 



Among the secondary structures independent of the fold are a 

 few small, vertical shear zones ^ in the quartzite on the east bluff of 

 Devil's Lake. The largest of these strikes N. 85 W. Since the south 

 wall of this fault is more intensely shattered than the north wall, and 



I See illustration on p. 17, RoUin D. Salisbury, "The Geography of the Region 

 about Devil's Lake and the Dalles of the Wisconsin," Bulletin No. 5, Wisconsin 

 Geological and Natural History Survey. 



