212 THE GEOLOGY OF MINNESOTA. 



[Aporliyolyte. 



times beyond the centre of the crystal. A vitreous feldspar is cut approximately 

 perpendicular to the axis n.. and affords extinction at 83, indicating andesine-oligo- 

 clase or oligoclase. The quartz of the matrix is micro-granitic, not poikilitic. A 

 section made perpendicular to the fluidal lamination presents a perlitic structure 

 throughout (plate I, figure 5), but in one parallel to it this structure is barely visible. 



Three sections. 



Mic. No. 140(2). This seems to le identical with Xo. 140(7), except that the 

 lamination is less regular. Brick red. 



Two poor sections. 



Mic. No. 140(3). Brick red, similar to Xo. 140(2), contains quartz and a glassy 

 feldspar. 



Three poor sections. 







Mic. No. 140(4). Dark brotcn, laminated in a manner similar to No. 140(1), 

 contains quartz and feldspar phenocrysts in the midst of a perlitic fluidal structure. 



Two poor sections. 



Mic. No. 140(5). liroini, or hroirnish gray, resembling in general aspect the 

 rock of the bulk of the Great Palisades, but still having a finely laminated fluidal 

 structure, which is generally not evident in that rock. It is crossed by veinings of 

 coarser secondary quartz. 



One section. 



Mic. No. 140(6). Broirn, hut failing through light brown to ralilix/t hroirn and to 

 a i/irtif huff /rliitc, like No. 140(12), the colors being irregularly distributed, but 

 governed by the fluidal lamination whenever it is preserved. The specimen, however, 

 appears to show that when plastic the magma had been folded and perhaps broken, 

 and molded upon itself. The rock contains quartz and opaque feldspar, but not the 

 glassy feldspar. 



One thick section. 



Mic. No. 140(7). Brick red, laminated. 



The slide consists essentially of three distinctly separate portions: 



1. Opaque, red, non-crystalline material. 



2. Minutely crystalline substance, giving aggregate polarization. 



3. Porphyritic crystals, clear and perfect. 



The first shows a fluidal structure very beautifully streamed about the porphyritic 

 crystals, but with this streamed structure is involved much of the minutely crystal- 

 line substance (2). In some cases No. 2 lies between the non-crystalline substance 

 and the crystals, and in other cases the non-crystalline substance is in immediate 

 contact with the crystals. The red substance is only a stained part of the slide, the 

 color being hematite red. It makes up most of the rock, but the mineral which has 



