COLLECTIONS IN ECONOMIC GEOLOGY AND METALLURGY. 115 



other varieties ^re recognized locally. Hematite and limonite are fre- 

 quently indiscriminately called hematite; they are also frequently dis- 

 tinguished as red and brown hematites. Occasionally, also, a single 

 physical name will include two or more chemical varieties; thus, honey- 

 comb ore may be either iiematite or limonite, while kidney ore may be 

 either hematite, limonite, or siderite. 



Iron ores are frequently classified according to the character of the 

 pig metal tliat they will produce, and tliis classification depends mainly 

 upon the presence or absence of impurities; thus, a steel ore must be 

 low in phos[)horus, while a cold short ore will be high in phosphorus, a 

 red short ore will be high in sul[)hur, and a neutral ore is one contain- 

 ing moderate amounts of both sulphur and phosphorus, but in such 

 proportions that they more or less neutralize each other. 



THE TENTH CENSUS IRON-ORE COLLECTION. 



Under the direct supervision of Prof. R. Pumpelly, the Tenth Census 

 made a very elaborate collection of the iron ores of the country. The 

 design of this collection was to take representative samples of each 

 variety of ore occurring at every mine that was worked during the cen- 

 sus year. Besides these, a complete sample of the ore as mined was 

 taken and submitted to a chemical examination. To these were added 

 illustrations of the associated rocks and minerals. This whole collection 

 embraced nearly four thousand specimens, and a suitable selection of 

 these has been placed ou exhibition. The exhibition series is arranged 

 upon a geographical basis. Several illustrations of manganese ore are 

 included in the collection. 



PISCATA(JUIS COUNTY. 



Ten specimens represent the ore mined b}' the Katahdin Iron Com- 

 pany, taken October 15, 1880. 



(1) Liiiionite, commouly called bo<; o.e. (42160.) 



(2) Limonite. (41349.) 



(3) Limonite. (42157.) 



(4) Limonite. (421.58.) 



(5) Limonite, rasv ore. (41350.) 



(6) Roasted ore. (42156.) 



(7) Pyrite, showing alteration to limonite, and ropre.senting the original sonrco 

 of the ore. (42159.) 



(8) Trap rock, occnrring in connection with the ore, containing a large percent- 

 age of sulphide of iron, cousiderahly decompo.sed. (41351.) 



(9) Trap rock, containing pyrrhotite ; probably the unaltered form of 41351. 

 (43662.) 



(10) Trap rock, probably the non-[)yritiferons portion of 41351. (42(l'J8.) 



VEHMOXT. 



.ADDI.SON COUNTY. 



(1) LimouiLc, surface ore, .Mouktou Mine, Mouktou, October 23, 1880. (42099.) 



