THE ADIRONDACK GRAPHITE DEPOSITS 39 



and contact deposits, while most of the bedded or blanket areas all 

 lie to the south. It may be that erosion, more severe in the south- 

 eastern portion of the region, has removed the contact zone rocks 

 in the section and has carried the present surface down to the 

 horizon of the graphite schists, while in the northern area can still 

 be seen patches of the Grenville in which graphite has been 

 developed by contact with igneous rocks under favorable tempera- 

 ture and pressure conditions. 



The contact deposits of graphite are usually very striking to 

 the layman and appear to be exceedingly rich and promising, but 

 the writer is convinced that they are too uncertain*, too pockety, and 

 too limited in extent to pay for mining. The milling of graphite is 

 still in the experimental stage. The bedded deposits, even though 

 much more uniform in character, afford difficult milling problems 

 but the treatment of contact ores is still more difficult because of 

 their greater variability. Even granted a large deposit of this form 

 of graphite, successful mining would be highly problematical. The 

 early workers on Lead hill were fortunate in that they realized 

 good prices for their product and had an unusually large deposit ; 

 and the operations were in charge of an inventive man. 



The important deposits of the northern area do not occur in veins. 

 It seems to be the universal opinion of graphite men in the Adiron- 

 dacks that veins, carrying graphite (deposited from aqueous 

 solutions) are common. On the contrary, they are extremely rare 

 and are always too small to be of commercial importance. Graphite 

 does occur, however, in the zone between an igneous rock and a 

 sedimentary one. The rocks most commonly so grouped are peg- 

 matite and limestone, which is the combination found at Buck 

 Mountain pond, Columbia, Crown Point, the " Woodchuck " work- 

 ings on Lead hill, Penfield pond, Mason, and in the Pottersville 

 properties. Deposits have also been formed by pegmatites in con- 

 tact with other members of the Grenville series; upon biotite- 

 hornblende schists, as in the case of the Betsy Cook and Towne 

 prospects ; upon amphibolite, as in the Young Lyon pit on Lead hill ; 

 and upon quartzite, as is found in the pits of the Columbia Graphite 

 Company and the Fryatt workings on Lead hill. 



The syenite (a granite low in quartz) has developed graphite in 

 contact with limestone as in the Gulf and Mammoth cave prospects. 

 And finally, the gabbro developed graphite when in juxtaposition 

 with a variety of sedimentary rocks, as at Split Rock. The writer 

 concludes then that most of the igneous rocks exposed in the 



