ADIRONDACK MAGNETIC IRON ORES 157 



Geology. The district lies within the main anorthosite area, 

 but not far from its western bounds. As delimited in the prelimi- 

 nary survey of J. F. Kemp, 1 the gneiss series occupies approximately 

 the western half of Newcomb township, the line of contact with 

 the anorthosite which extends over the eastern half trending some- 

 what west of north. It is not easy to fix accurately the limits of 

 the formations owing to the drift which chokes the valleys and 

 reaches well up the slopes of the ridges. Anorthosite has been 

 found by the writer to outcrop on Santanoni mountain, about 5 

 miles directly west of Lakes Sanford and Henderson, so that it prob- 

 ably continues in unbroken mass that far. The gneiss series first 

 appears on the shores of Newcomb lake and in the east -west valley 

 occupied by Rich and Harris lakes, whence it stretches westward 

 as far as the confines of the Adirondacks. 



The gneiss series bordering the anorthosite has been subjected 

 only to a cursory examination. Apparently it consists of a com- 

 plex in which both sedimentary and igneous types are represented. 

 The former have particularly strong development around Newcomb, 

 where there is one of the largest Grenville exposures in the interior 

 of the Adirondacks. They comprise the usual rusty micaceous 

 and hornblendic gneisses and schists, with interfolded belts of 

 crystalline limestone carrying graphite and other characteristic 

 minerals. A limestone ledge on the east side of Newcomb lake 

 was a source of flux for the early furnace operations. Professor 

 Cushing in his recent mapping of the geology of the Long Lake 

 quadrangle has noted the presence of extensive masses of syenite 

 and granitic gneisses, and it is not unlikely that upon further investi- 

 gation they will be found to constitute an important part of the area 

 farther east along with the Grenville formation. The region 

 about the mines is included in the Santanoni quadrangle which 

 adjoins the Long Lake sheet on the east. 



The principal interest in connection with the iron ores is 

 attached, of course, to the anorthosite. Where exposed near the 

 mines this is generally a very typical variety of the rock as devel- 

 oped in the Adirondack region. It consists essentially of labra- 

 dorite in grayish or bluish black crystals, that occasionally exhibit 

 a play of colors on cleavage surfaces. The crystals are generally 

 large, up to 3 or 4 inches in length, and are closely interwoven 

 with a coarsely granitic texture. While as a rule the feldspar 

 constitutes practically the only mineral observable in hand speci- 



1 Preliminary Report on the Geology of Essex County. N. Y. State Mas. 

 4Qth An. Rep't. 1898. 2:604. 



