ADIRONDACK MAGNETIC IRON ORES III 



massive habit with the regular jointing peculiar to deep seated 

 intrusives. While there are no supporting evidences of inclusions 

 of contact effects, it is regarded as igneous and probably later than 

 the augite gneiss. 



A second type of granitic gneiss, related to the preceding in 

 mineral character but possessing a thorough cataclastic structure, 

 was found on Birch hill between Lyon Mountain and Upper Cha- 

 teaugay lake. The feldspar consists of microperthite, orthoclase 

 and microcline, all of which have been crushed and finely granu- 

 lated, though an occasional larger crystal particle is inclosed in the 

 crushed materials. The quartz is drawn out into thin bands. 

 Much magnetite occurs in shreds and irregular grains distributed 

 through the mass or more frequently aggregated along parallel 

 lines which may be continuous for some distance. Except for a little 

 secondary biotite there are no ferromagnesian minerals present. 



Hornblende schist. A dark hornblende schistose rock is occa- 

 sionally found in small patches and lenses surrounded by the augite 

 gneiss. It has a more schistose appearance than any of the other 

 rocks and is also conspicuously banded. The principal mineral is 

 dark green hornblende. The feldspar includes both orthoclase and 

 plagioclase in about equal proportions. The remaining minerals 

 comprise scapolite and titanite, the latter constituting at times 

 fully 10 per cent of the mass, and small quantities of augite, biotite, 

 magnetite and apatite. 



Lithologically the schist is quite like the schists that accompany 

 the series of sedimentary gneisses and the crystalline limestones. 

 No exposures of limestone were found, but in limited areas like 

 those at Lyon Mountain it is often absent. At the Williams pit 

 the schist forms both walls of the deposit as a comparatively thin 

 band that is intercalated in the augite gneiss with the axis of 

 extension parallel to the general strike. It is seamed by layers of 

 lighter colored gneiss and shades off at the edges into the augite 

 gneiss through a gradual exchange of the hornblende for the augite 

 and the appearance of microperthitic feldspar. On the hanging 

 side of the deposit, the schist incloses a seam that is made up 

 almost entirely of garnet, a black, nearly opaque submetallic variety, 

 evidently high in iron. The same schist was noticed in the walls at 

 the Dickson open cut, and much of it occurs in the rock dumps at 

 Parkhurst shaft though not observed there in place. These obser- 

 vations indicate that a considerable mass of the rock, probably 

 in interrupted bands or lenses, is inclosed by the augite gneiss in 

 proximity to the ore zone. 



