92 THE CRYSTAL PALLS IRON-BEARING DISTRICT. 



At a point about 100 feet higher and three-fourths of a mile distant, on 

 the very northwest flank of the same hill, at N. 1725, W. 775, from the south- 

 east corner of sec. 4, T. 44 N., R. 32 W., there is a small ledge of schistose 

 porphyry, macroscopically and microscopically similar to those to the south- 

 east of it, and with its schistosity striking N. 20° W. and dipping 80° SW. 

 The striking agreement in strike, dip, and general character of these two 

 separated outcrops points to their being merely isolated portions of the 

 same mass. There seems to be no discrepancy between the dip and strike 

 of the schistosity and that given above for the bands. 



The most striking macroscopical characteristic of these mashed por- 

 phyry flows is the occurrence of phenocrysts in a schistose and beautifully 

 banded rock. These phenocrysts stand out clearly from the groundmass 

 in all cases. The general appearance of the rocks is that of the well-known 

 very dense banded halleflintas of Elfdalen, Sweden. The bands vary in 

 color, ranging on the weathered surface from light creamy white, tln-ough 

 light greenish, to red and almost black. The rocks which have very light 

 colored weathered surfaces are always bluish black on a fresh fracture, and 

 very dense, and those weathering red are usually cream colored on freshly 

 fractured faces. Many of the areas which appear macroscopically to be 

 single phenocrysts are resolved under the microscope into tangled groups 

 of individuals, though in rare cases the individuals show the impeifect 

 radial arrangement rather frequent in medium-grained micropegmatitic 

 rhyolite-porphyries. 



The feldspar has undergone considerable alteration. In the least- 

 changed grains there is a cloudiness caused by numerous indeterminable 

 specks, probably of iron oxide, which give a reddish tinge to the mineral. 

 Further changes result in the production of muscovite and epidote, with 

 biotite in rare cases, accompanied by the obliteration of the twinning 

 lamellae. The greater part of the phenocrysts seem to be orthoclase, 

 though associated with them are found pieces which show indistinct traces 

 of the polysynthetic twinning of plagioclase feldspar. The feldspars 

 exhibit marked strain eff"ects, especially in their flattening into long oval 

 and spindle-shaped areas. Some crystals have been broken and separated 

 perpendicular to the direction of the schistosity. The spaces between the 

 fragments are filled with secondary muscovite, quartz, and feldspar. Sur- 

 rounding the phenocrysts — that is, between the phenocrysts and the ground- 



