M'EIDilAN — QUARTZ KERATOPIIYRE OF BARABOO BLUFFS 45 



contact zone of schists in the southwest i- of the northeast i 

 of Sec. 22, there is an outcrop of volcanic breccia ' frag- 

 ments in which usually have the typical flow structure 

 about them. A similar exposure '^ occurs at the contact 

 near the center of Sec. 22. The included fragments in the 

 rock of both the above localities are of a hard pink rock, and 

 unlike the schist in which they are imbedded they are rel- 

 atively unaltered. In the field these fragments were taken 

 to be a pink quartzite, but the microscopic slides show them 

 to be an acid porphyry. 



The best exposures of breccia,' however, were found on 

 the north side of the road opposite Mr. Hewitt's house, in 

 the northeast i of the northwest i of Section 21. This 

 outcrop exhibits a schistosity, the dip of the cleavage 

 planes being 75° to the north and the strike a little north 

 of east. The fragments forming this breccia are much 

 larger than those found in the other schists and are usually 

 angular and elongated in the plane of schistosity. They 

 vary in size from an inch to a foot in diameter, and were at 

 once taken to be of eruptive origin. 



The fragments of this breccia represent several rock 

 varieties. One is brownish pink in color and is composed 

 almost wholly of secondary spherulites which are from 

 two-eighths inch to three-eighths inch across. On the 

 surface of the exposure these secondary spherulites have 

 weathered out, leaving cavities lined with quartz, which 

 makes them appear much like amygdaloidal cavities. An 

 other variety is a brownish gray schistose rock which 

 contains many feldspar phenocrysts, some of which have 

 weathered out leaving cavities filled with black ferruginous 

 material. Other fragments are composed of a dull lead 

 colored rock, slightly schistose and having no phenocrysts. 



A large number of loose blocks * was found in the road 



1 Specimens 3084 and 3085. 



2 Specimen 3081. 



3 Specimens 309 J, 3094. 

 ■* Specimen 3096 . 



