42 BULLETIN OF THE UNIVERSITY OP WISCONSIN 



The contact between the quartz keratophyre and the 

 Cambrian sandstone and conglomerate is well shown in the 

 northwest i of Sec. 21. At this place a narrow strip of 

 the conglomerate projecting from the large sandstone area 

 to the west, lies in horizontal beds upon the dipping edges 

 of the sericite schist (Fig. 1, Sec. IV). These schists dip 

 to the north at an angle of 75° or SO'', essentially the same 

 as those farther south at the contact with the quartzite. 

 Farther west from this tongue of conglomerate, in a ravine 

 which marks the eastern boundary of the massive sand- 

 stone area, the contact is again well shown, the horizontal 

 sandstone lying upon the upturned edges of the sericite 



schist. 



Absence of Bedding.— This rock does not, like the quartz- 

 ite, exhibit stratification, but on the contrary all traces of 

 bedding are entirely wanting. It does, however, at the 

 contact form a zone of schists from 150 to 200 feet in 

 width, and also in a considerable area in the north- 

 west i of Sec. 21, schists are foand. The cleavage 

 planes of these schists always dip to the north at an angle 

 of 75° or 80°. Irving ' in describing this area, speaks of 

 the schists, and whenever he does so he invariably men- 

 tions the clearly defined bedding which the rocks show. 

 Although he was one of the first geologists who later 

 learned to recognize the importance of distinguishing 

 schistosity from stratification, it is evident that he com- 

 mitted the common error of taking the one for the other 

 in this region. 



Tyjjes of Rock.— The eruptive rock as it appears in the 

 field exhibits marked local variations, due both to condi- 

 tions in the eruptions of the magma and to dynamic action 

 since the general outflow. These differences allow a classi- 

 fication of the rock into three distinct types, which will be- 

 described separately. These types are normal quartz kerat- 

 ophyre, sericite schist, and volcanic breccia. 



1 Geol. of Wis , Vol. II; pp. 513 515. 



