174 EEPORT OF NATIONAL MUSEUM, 1899. 



J. PosTLETHWAiTE. The Borrowflale Plumbago; its Mode of Occurrence and Probable 

 Origin. 



Proceedings of the Geological Society of London, Session, 1889-1890, p. 124. 

 On the formation of Graphite in contact-metamorphism. 



American Journal of Science, XLII, 1891, p. 514. Review of article in 

 Berichte der Deutschen chemischen Gesellschaft, XXIV, p. 1884, 1891. 

 W. Luzi. Zur Kenntniss des Graphitkohlenstoffes. (Berichte der Deutschen Chem- 

 ischen Gesellschaft, XXIV, pp. 4085-4095. 1891.) 



Neues Jahrbuch fiir Mineralogie, Geologie und Paleontologie. 1893. II, Part 

 2, p. 241. (Abstract.) 

 E. Weinschenk. Zur Kenntniss der Graphitlagerstatten. Chemisch-geologische 

 Studien von Dr. Ernst Weinschenk. 



1. Die Graphitlagerstatten des bayerischen Grenzgebirges. Habilitations- 

 schrift zur Erlangung der venia legendi an der K. technischen Hochschule. 

 Miinchen, 1897. 

 Fkanz Kretschmee. The Graphite Deposits of Northern Moravia. 



Transactions of the North of England Institute of Mining and Mechanical 

 Engineer, XLVII, 1898, p. 87. 



2. Sulphur. 



Color of the mineral when pure yellow, sometimes brownish, red- 

 dish, or gray through impurities. Hardness, 1.5 to 2.5. Specific 

 gravity, 2.05. Insoluble in water or acids. Luster resinous. Occurs 

 native in beautiful crvstals (Specimens Nos. 53115, 53116, and 60660, 

 U.S.N.M.) or in massive (Specimens Nos. 16092, 60819, U.S.N.M.), 

 stalactitic and spheriodal forms (Specimens Nos. 57137 and 60861, 

 U.S.N.M.). Once seen the mineral is as a rule readily recognized, 

 and all possible doubts are set at rest by its ready inflammability, 

 burning with a faint bluish flame and giving the irritating odors of 

 sulphurous anhydride. In nature often impure through the presence 

 of clay and bituminous matters; sometimes contains traces of selenium 

 or tellurium (Specimens Nos. 60856 and 60861, U.S.N.M.). 



Origin and mode of occurrence. — Sulphur deposits of such extent as 

 to be of economic importance occur as a product of volcanic activity, 

 or result from the alteration of beds of gypsum. On a smaller scale, 

 and of interest from a purely mineralogical standpoint, are the occur- 

 rences of sulphur through the alteration of pyrite and other metallic 

 sulphides. 



As a product of volcanic action sulphur is formed through the oxida- 

 tion of hydrogen disulphide (HoS), which, together with steam and 

 other vapors, is a common exhalation from volcanic vents and solfataras. 

 Such deposits on a small scale may be seen iucrusting fumaroles in the 

 Roaring Mountain (Specimen No. 72872, U.S.N.M.) or associated with 

 the sinter deposits of the Mammoth Hot Springs in the Yellowstone 

 Park (Specimen No. 72877, U.S.N.M.). It may also be produced 

 through the mutual reaction of hydrogen disulphide (HgS) on sulphuric 

 anhydride (SO,), the product being sulphur (S) and water (H^O) as 



