Review of Recent Geological Literature, 185 
but widely spread, group is acid in composition, and these are com- 
posed largely of quartz and glaucophane, with mica and sometimes 
albite. These are derived from cherts, quartzites or quartzose shales 
and sandstones. The existence is indicated of a third, still smaller 
group of intermediate mineralogical composition, and chemically like 
the diorites. The glaucophane schists are apparently the result or 
both regional and contact metamorphism, and in many regions they oc- 
cur together. This last seems to be the rule in glaucophane schist 
areas of any size, and where only the one kind is found the area is 
apt to be small." c. h. w. 
The Mode of Occurrence of Topaz Near Otiro Preto, Brazil. By Or- 
viLLE A. Derby. (Am. Jour. Sci., 161. 25-34.) 
The article gives the results of a study of the associated earths 
and rocks where the topaz is found. The mineral itself is found in a 
dark-colored earth, thought, from its mineralogical character and its 
geological relations, to represent the remains of an igneous dike in 
which the topaz was an original mineral. What the exact nature of 
the igneous dike was cannot be told on account of its state of ex- 
treme alteration. c. H. \v. 
Carnotite and Associated Vanadiferous Minerals in Western Colorado. 
By W. F. HiLLEBRAND and F. Leslie Ransome. (Am. J. Sci., 160. 
120-144.) 
The paper embodies the results of investigations concerning the oc- 
currence and nature of the uranium and vanadium ores of western 
Colorado. A somewhat detailed description of the various ore de- 
posits is given by Dr. Ransome from a study of the region made by him 
and Dr. A. C. Spencer. He concludes that the ores are recent im- 
pregnations in the sandstones. The chemical researches made and re- 
corded by Dr. Hillebrand furnish, not only valuable data concerning 
the composition of the ores and their constituent minerals, but afford 
the chemist excellent descriptions of the analytical methods involved 
in the analysis of the uranium and vanadium ores. The summary made 
by the authors is as follows : "The body called carnotite is probably a 
mixture of minerals of which analysis fails to reveal the exact nature. 
Instead of being the pure uranyl-potassium-vanadate, it is to a large 
extent made up of calcium and barium compounds. Intimately mixed 
with it and entirely obscured by it is an amorphous substance — a sili- 
cate or mixture of silicates — containing vanadium in the trivalent state, 
probably replacing aluminum. The deposits of carnotite, though dis- 
tributed over a wide area of country, are, for the most part, if not 
altogether, very superficial in character and of recent origin. The 
green coloring and cementing material of certain sandstones near 
Placerville, Colorado, is a crypto-crystalline alumino-vanadio-potassium 
silicate resembling roscoelite, but with the percentage proportions of 
AI2O3 and ViOs reversed. It constitutes over 25 per cent, of the sand- 
stone at times, and contains nearly 13 per cent, of V2O3. the latter 
amounting in the maximum case observed to 3.5 per cent, of the sand- 
stone. As yet these highly vanadiferous sandstones have been found 
