l70 REPORT ()¥ NATIONAL MUSEUM, 1S99. 



plates of plumbao'o. At other times the mineral is so tineW dissemi- 

 nated as to give a bluish-gray color to the limestone, and the distribu- 

 tion of the l)ands thus colored seems to mark the stratification of the 

 rock. Further, the plumbago is not (!onfined to the limestones; large 

 crystalline scales of it are occasionally disseminated in pyroxene rock 

 or pyrallolite, and sometimes in quartzite and in feldspathic rocks, or 

 even in magnetic oxide of iron. In addition to these bedded forms, 

 there are also true veins in which graphite occurs associated with cal- 

 cite, quartz, orthoclase, or pyroxene, and either in disseminated scales, 

 in detached masses, or in bands or layers separated from each other 

 and from the wall rock by feldspar, pyroxene, and quartz. Kemp 

 describes ^ the graphite deposit near Ticonderoga, New York (Specimens 

 Nos. 37825, 66759, U.S.N.M.), as in the form of a true fissure vein, 

 cutting the lamination of the gneissic walls at nearl}^ right angles. 

 The wall rock is a garnetiferous gneiss, with an east and west strike, 

 and the vein runs at the "big mine'' north 12° west, and dips 55° west. 

 The vein filling, he says, was evidently orthoclase (or microcline) with 

 quartz and biotite and pockets of calcite. Besides graphite, it con- 

 tained tourmaline, apatite, pyrite, and sphene. 



Walcott" describes the graphite at the mines 4 miles west of Hague, 

 on Lake George, New York, as occurring in Algonkian rocks, and as 

 probably of organic origin. 



At the mines the alternating layers of graphite shale or schist form a bed varying 

 from 3 to 13 feet in thickness. The outcrop may be traced for a mile or more. The 

 garnetiferous sandstones form a strong ledge above and below the graphite bed. The 

 appearance is that of a fossil coal bed, the alteration having changed the coal to 

 graphite and the sandstone to indurated, garnetiferous, almost quartzitic sandstones. 

 The character of the graphite bed is well shown in the accompanying plate, from a 

 photograph taken by me in 1890. It is here a little over 9 feet in thickness and is 

 formed of alternating layers of highly graphitic sandy shale and schist. [See Plate 3.] 



According to J. Walther^ the Ceylonese graphite (Specimens Nos. 

 66857, 62073, U.S.N.M.) occurs in coarsely foliated or stalky masses in 

 veins in gneiss which, where mined, is decomposed to the condition of 

 laterite. The veins are regarded as true fissures, and vary from 12 to 

 22 cm. (about 4i to 8f inches) in width. 



The graphite of Northern Moravia occurs in gray to ])lack crystal- 

 line granular Archa?an limestone interl)edded with amphibolites and 

 muscovite gneiss, the limestone itself being often serpentinous, in this 

 respect apparently resembling the graphitic portions of the ophical- 

 cites of Essex County, New York. (Specimen No. 70081, U.S.N.M.). 

 The material is quite impure, showing on the average but 53 per cent 

 of carbon and 44 per cent of ash, the latter being made up largely of 



^ Preliminary Report on the Geology of Essex County, Contributions from the Geo- 

 logical Department of Columbia College, 1893, pp. 452, 453. 

 2 Bulletin of the Geological Society of America, X, 1898, p. 227. 

 ^Records of the Geological Survey of India, XXIV, 1891, p. 42. 



