July 20, 1900.] 



SCIENCE. 



95 



When graphite appears in metamorphic 

 rocks it has been generally considered in 

 America and until recently abroad as well, 

 to have been derived from organic matter 

 originally in the sediments, but in more re- 

 cent years investigations have been carried 

 out which throw some doubt on these con- 

 ceptions. Graphite, considered purely as 

 a mineral has come in for a large share of 

 attention and some writers have even dis- 

 tinguished three varieties, viz, graphite, 

 graphitite and graphitoid, depending on dif- 

 ferences of physical structure or behavior 

 with oxidizing reagents. Weinschenk, of 

 Munich, has however quite conclusively 

 shown in a recent paper, that all are varie- 

 ties of graphite proper, differing only in 

 fineness of scales or perfection of crystalline 

 form. All true graphite when warmed with 

 fuming nitric acid and potassium chlorate 

 changes into yellow, transparent crystals, 

 possessing the same hexagonal form as the 

 original and exhibiting while wet and fresh, 

 the optical properties of a negative uniaxial 

 crystal. These are called graphitic acid. 

 They yield by analysis somewhat variable 

 results but they are known to have assumed 

 over 40 per cent, of oxygen and about 1.5 

 of hydrogen. Other dark amorphous forms 

 of carbon dissolve in fuming nitric acid 

 and potassium chlorate to a brown liquid. 



So far as my observations go, all the oc- 

 currences on the east are true graphite. I 

 have not noted any other form of carbona- 

 ceous matter, but in the marbles quarried 

 at Gouverneur there are cloudy veinings, 

 which may not be the mineral. 



In a valuable paper on the graphite de- 

 posits along the border of Bavaria and Bo- 

 hemia, usually referred to as the Passau 

 district, "Weinschenk* has shown that the 

 graphite occurs in a much decomposed 

 gneiss, in lenticular enrichments, the best 



* Weinschenk, E., 1897. Vorkomnisseans Graph- 

 itlagerstiitten noidostlicli von Passau. Zeit. /. Eryst. 

 and Jfm., 1897, XXVII., 135. 



of which are associated with crystalline 

 limestone, and all of which follow the con- 

 tact line of a huge granite intrusion and at 

 small distances from it. When the contact 

 is left the graphite deposits become leaner 

 and leaner and finally die out. The graph- 

 ite fills all manner of cracks in the min- 

 erals of the containing rock and the inter- 

 stices between the minerals and may even 

 amount to 60 or 70 per cent, of the mass. 

 Weinschenk concludes that the graphite 

 has not come from original deposits in the 

 gneiss and limestone, but from gases emitted 

 at moderate temperatures from the granite 

 and which penetrated into all the small 

 cavities of the gneiss and limestone. The 

 most probable constituents of the gases are 

 thought to be carbonic oxide, carbonates of 

 iron and manganese, cyanides of titanium, 

 carbonic acid and water. All contributions 

 from the gneiss and limestone and all other 

 forms of carbonaceous matter are specifi- 

 cally ruled out. 



Into the abundant other literature of 

 graphite, especially as concerns Ceylon or 

 other productive regions, I do not go as the 

 important point before us is to determine 

 the significance of the graphite in the Adi- 

 rondack rocks, and to decide whether its 

 carbon has been introduced by the erup- 

 tives. Of eruptives there is no lack, if not 

 always in immediate association with the 

 graphitic rocks, at least within short dis- 

 tances. 



In any conclusions the following condi- 

 tions must be met : 



1. The graphite is in all the crystalline 

 limestones, sometimes richly. 



2. It is most coarsely crystalline in the 

 pegmatitic bunches of silicates, which of all 

 sizes from that of the finest to that of many 

 cubic yards, are so richly present in the 

 limestones. 



3. It is richly developed in the quartzite 

 at Hague and appears in many others in less 

 amount. 



