46 BULLETIN OP THE UNIVERSITY OP WISCONSIN 



near the house of Mr. Montgomery, in the southeast i of 

 the southeast i of Section 17. This rock on its weath- 

 ered surface shows very clearly the flow structure about the 

 included fragments. Unlike the fragment-bearing rock in 

 situ this is not markedly schistose, is not much altered, 

 and the included fragments are few. The weathered sur- 

 faces seem to give evidence of a few large and widely sep- 

 arated spherulites, but none of these were included in the 

 sections which were prepared. An outcrop of fresh brec- 

 cia ' in the northwest i of the northwest i of Sec. 21, 

 shows numerous phenocrysts of feldspar intermingled with 

 small rock fragments. 



Conclusions Drawn from Field Study.— The work in the 

 field shows the areal extent of the eruptive rock to be some- 

 what greater than was formerly supposed. A marked 

 difference is found in the rock as it outcrops ia various 

 places. The contact closely conforms in direction for the 

 greater part of the distance, with the strike of the under- 

 lying quartzite beds and the dip of the cleavage planes 

 of the contact schists agrees with the dip of the quartzite. 

 Volcanic breccia occurs in considerable quantity in various 

 localities. All the phenomena observed during the field 

 study are evidence that the porphyry in its several phases 

 represents a volcanic outflow which took place over beds 

 of quartzite. During the elevation which followed, the 

 overlying eruptive rock was in j^art metamorphosed into 

 schist. 



III. Microscopic Geology. 



The structure of the rock, as it is presented by the 

 microscopic sections in the laboratory confirms the evidence 

 gathered in the field for the extrusive character of the 

 quartz keratophyre. The porphyritic structure is developed 

 in all the types of rock, being well shown in the volcanic 



1 Specimen 3079. 



