170 The American Naturalist, Leesa 
of calcite separates from all solutions of pure carbonate in dilute car- 
bonic acid at low temperatures. In general, under different condi- 
tions of formation, differently habited crystals are produced. More 
over, different proportions of impurity in the solution affect differently 
the resulting crystals, as well as the rapidity with which they grow. 
Contrary to the prevalent belief, however, the presence of calcium bi- 
carbonate in a solution of the mono-carbonate exerts but little influ- 
ence upon the complexity of the calcite crystals formed. The article 
is long, and is a thorough discussion for the subject treated. 
North Carolina Quartz Crystals.—Gill"™ supplements Von 
Rath’s study of North Carolina quartz crystals by describing some new 
forms and giving the results of etching spheres made from simple left- 
handed crystals with hydrofluric acid and hot sodium carbonate. 
The conclusions of his crystallographic study are to the effect that the 
mean of the measurements of 38 crystals give an axial ratio a: ¢ =I: 
1.1018. This ratio, which is larger than usual for quartz, is ascribed 
to the lengthening of the ¢ axis brought about by impurities included 
within the crystals. All the crystals investigated were smoky quartzes, 
whose axial ratio approaches that of the Swiss crystals, and is larger 
than that of the Riesengrunde occurrences (1: 1.0996). The crystal- 
lazition is trapezohedral-tetartohedral, which may be best regarded a8 
a combination of trapezohodral hemihedrism and hemimorphism with 
respect to the lateral axes. The author notes the effect of various 
influences upon the development of the planes observed on quartz, and 
closes his paper with a discussion of crystal structure. The proper 
ties of quartz are explained upon the assumption of a molecule of 
SiO, in which Si is in the center of a regular tetrahedron, from whose 
upper and lower edges the oxygen exercises its influence. 
Two New Books.—Hatch’s mineralogy™ is an elementary pi 
book for the use of beginners in the study of minerals. The book 
gins with a very elementary treatment of the systems of nine 
based in the notion of symmetry. It defines the terms made ue : 
describing the physical properties of minerals and ends with seventy: 
five pages on systematic mineralogy. The classification U FE 
arbitrary one—the rock-forming minerals being first discussed, the 
the ores, next the salts and other useful compounds and finally 
Zeits. f. Kryst., XXII, p. 97. yiii 
“Mineralogy by F; H. Hatch, London, Whittaker & Co., 1892, FP® 
and 22 
