Hies — Geology of Oranoe County. 



461 



parent mass is exposed anywhere, the writer is unable to say, as, in the time 

 at his disposal, he was unable to examine the Highland region in sufficient 

 detail. 



The distribution of the dikes is not confined to the area of Highland or 

 northwestern Woodbury townships. A narrow porphyritic camptonite dike 

 cuts the gneiss northwest of Arden, along the road from Arden to the O'Neil 

 mine (490). 



At the west end of Little Long pond southeast of Southfield, is a curious 

 little group of five such dikes, which may be branches of the same 

 dike. These do not penetrate the gneiss to any extent, but are mostly 

 in a pegmatite vein which cuts it. They are all composed of idiomorphic 



Figure 23. Section of hypersthene-gneiss from 

 west side of Sterling lake. The hypersthene is 

 marked with interrupted striations ; the mag- 

 netite forms irregular black grains and the 

 pyrite square ones. The plain white is plagio- 

 clase, containing inclusions of apatite, mag- 

 netite and pyrite. (Specimen No. 346.) 



Figure 24. Section of gneiss along fault-line in 

 limestone quarry, N. E. of Arden, showing 

 large fragments of quartz and feldspar (ortbo- 

 clase) in a crushed matrix of the same min- 

 erals, cemented by limonite and decomposed 

 biotite(f). (Specimen No. 273.) 



hornblendes in a ground-mass of plagioclase with grains of magnetite. The 

 grain becomes finer as the width of the dike decreases. The gneiss strikes 

 N. 20" E., with a vertical dip. The dike nearest the lake is two feet wide 

 and strikes N. TO'' W.; the next one, one foot wide, striking N. 50" W.; 

 the third, N. 70" W.; the fourth, K 50° E. and two inches wide; the fifth, 

 N. 30° W., and four inches wide. The camptonite dike which intersects 

 the ore-body at the O'Neil mine is an olivine camptonite. The ground-mass 

 is composed of idiomorphic hornblende and plagioclase, with subordinate 

 magnetite. There are also phenocrysts of olivine. Scattered through the 

 rock are cavities filled with calcite which may result from the alterations of 



