THE MINING AND QUARRY INDUSTRY I9II IO5 



advantage over most in their average tenor. They are furthermore 

 exceptionally situated for economic exploitation, with convenient 

 shipping facilities, cheap electric power available, and efficient labor 

 to be had in the district. 



The derivation of the ores is an interesting problem that need not 

 be given detailed treatment in this place. The apparent close 

 association of the zinc and talc deposits may be pointed out as a 

 feature of practical importance to exploration and it seems very 

 likely to reflect some underlying geological principle. The geologi- 

 cal relation, if such exists, is probably between the tremolite and the 

 zinc ores rather than between the latter and the talc itself which is 

 an alteration product of the tremoHte. The extensive development 

 of tremoHte in belts within the limestone is regarded by the writer 

 as the work of underground circulations which have brought in 

 silica and perhaps also a part of the magnesia necessary for the 

 conversion of the lime carbonate to the magnesia-lime silicate. 

 These circulations, it is reasonable to suppose, may have carried 

 other ingredients including zinc, lead and iron which have gone to 

 form the metallic deposits. 



The zinc deposits have the general appearance of replacement 

 bodies rather than the fillings of open fissures or cavities. In most 

 places their boundaries are not clean cut but are in the nature of 

 transition zones shading off gradually into the limestone. The lens 

 of compact ore which has been under recent development shows, 

 however, fairly sharp contacts. The internal structures are not 

 those characteristic of open-fissure fillings as there is no appearance 

 of banding or crusts or drusy cavities lined with crystallized 

 minerals. The compact granular nature of the ore suggests deposi- 

 tion at considerable depth and under pressure. In that event it may 

 be inferred also that the deposits are very old, possibly of Precam- 

 brie age. Erosion in this part of the Adirondack region seems to 

 have been comparatively slight since Cambric times and has been 

 mainly effective in removing the mantle of Paleozoic sediments 

 which now are only found in the bordering area. 



