Geology and Natural History. 243 



small quantities of white to grayish-brown quartz and of white 

 felspar, and a very small quantity of a green chromiferous sili- 

 cate. It has a velvet-black color, and is opaque ; in very thin 

 sections, however, it is translucent, and brownish-red by trans- 

 mitted light. The luster is submetallic. It breaks with an 

 uneven fracture ; is very brittle ; and affords a grayish inclining 

 to blackish, brown streak. It is non-magnetic. Its specific 

 gravity, at 15*5° C, is 4*239. Before the blowpipe, both in the 

 outer and inner flame, it remains unchanged. With borax, it 

 gives a bead which, in the oxidizing flame, is yellow while hot, 

 and pure green when cold ; and in the reducing flame, is of a fine 

 emerald-green color, both hot and cold. With salt of phos- 

 phorus it yields a limpid glass which, in the oxidizing flame, 

 while hot-, appears yellowish, and on cooling, assumes a fine green 

 color ; whilst in the reducing flame, the bead is greenish while 

 hot, and bright emerald-green when cold. It is not acted upon 

 by acids. 



The mean of two very closely concordant analyses, conducted 

 by Mr. R. A. A. Johnston, showed this mineral to have the fol- 

 lowing composition : 



Chromium sesquioxide 55*90 



Alumina 13*83 



Ferrous oxide . _ _ _ 14*64 



Magnesia _ 15*01 



Silica 0*60 



99*98 



The presence of the silica would indicate that, notwithstand- 

 ing the great care exercised by Mr. Johnston in the preparation 

 of the material employed by him for analysis — a matter attended 

 with considerable difficulty, even with the aid of heavy solu- 

 tions — the same was, nevertheless, not absolutely free from all 

 traces of some of the associated minerals. 



2. Still Rivers of Western Connecticut ; by William Herbert 

 Hobbs. Bull. Geol. Soc, vol. xiii, pp. 17-26, pis. i-ii. — In this 

 paper two rivers, viz. : Still River between Danbury and New 

 Milford and Still River at Winsted, are described and their life 

 history traced. 



3. Petrographisches JPraktikuni ; by R. Rheinisch. Erster 

 Theil : Gesteinbildende Mineralien. Pp. 135, 8vo, 82 figs, in 

 text. Berlin, 1901 (Gebr. Borntraeger). — The author states in 

 his preface that this work is intended for those who desire only a 

 general knowledge of the subject or wish to take it up by them- 

 selves. After a preliminary description of the making of thin 

 sections and the microscope, the various important rock-making 

 minerals are treated, with the introduction when necessary of 

 optical or chemical means of discrimination. The work presup- 

 poses some knowledge of mineralogy, optics and chemistry. It 

 is designedly of elementary character, for the use of beginners, 

 and in this field should prove useful. l. v. p. 



