262 EDWARD STEIDTMAN 



foot in thickness, separated by a thick bed of quartzite. Both bedding 

 and diagonal strike joints are present in these beds. The beds 

 strike N. 65 E., and dip 20 degrees north. The diagonal strike 

 fractures are closely spaced y"-shaped fractures, which are nearly 

 parallel to the bedding plane near the upper and lower surfaces of 

 the bed, while at the center of the bed their dip is 50 degrees north. 

 Some of these y^-shaped diagonal strike joints are connected with 

 north-dipping diagonal strike joints in the strong quartzite beds. 

 Another set of diagonal strike joints intersects the ^-shaped set. 

 Fig. I shows the relation of the joints connected with the folding in 

 thin, weak beds interstratified with strong, thick beds. 



The igneous rocks both on the North and the South Range have 

 joints related to the folding of the range. These joints strike parallel 

 to the strike of the quartzite formation and are vertical or nearly 

 vertical closed joints. 



Locally intense dynamic activity accompanying the folding of the 

 range has deformed the formations by fiowage, resulting in the devel- 

 opment of a schist. On the North Range, at the Lower Baraboo 

 Narrows, in a zone about one hundred feet wide following the con- 

 tact of the quartzite and the ryolite to the north, the ryolite and some 

 of the quartzite have been rendered schistose. The strike of the 

 cleavage conforms to the strike of the bedding of the quartzite. Its 

 dip is vertical or nearly vertical in the quartzite. In the ryolite it 

 varies from vertical to 65 degrees north. 



SECONDARY STRUCTURES NOT RELATED TO THE FOLDING 

 OF THE RANGE 



The joints which are most conspicuous in the Baraboo quartzite 

 formation, about 80 per cent, of the joints of the South Range, and 

 approximately 60 per cent, of the joints of the North Range are not 

 related to the folding of the range. Their strike and dip relations 

 differ radically from the joints and secondary structures which are 

 connected with the folding in that their strike and dip relations are 

 independent of the strike and dip relations of the quartzite formation. 

 These independent joints usually occur in sets at right angles to each 

 other. They have considerable continuity both along the strike and 

 the dip, and stand out as gaping, open, vertical, or nearly vertical 



