700 The American Naturalist. [ August, 
to trace the symmetry of the particle to the symmetry of the chemical 
molecule as its source. According to the conception of most chemists 
the carbon atom may be represented by a point with four bars extend- 
ing toward the four corners of a circumscribed tetrahedron. The sym- 
metry of the carbon molecule is thus comparable with the symmetry 
of the crystallized carbon—diamond. With this suggestion as a basis 
the author shows how the crystallization of graphite and of some of 
the carbonates may be explained, but at the same time he confesses 
that few practical results can follow from the suggestion until we know 
more about the composition of solid substances. 
Notes.—An attempt to discover the reason for the variation in the 
pyramidal angles of arsenopyrite and to settle its composition has - 
been made by Weibull,” who has examined crystals from Silfberg, 
Delane, and other localities in Sweden, and from the well-known i 
occurrences in Europe. Among the Silfberg crystals three types were - 
recognized, on the first of which the predominant forms are œ P an ‘ 
P Their axial ratio is .6841 : 1 : 1.1910, and composition (Fe Co - 
Ni) (S As), On the second type the same forms are observed with a 
the addition of PZ, but the — are usually prismatic parallel to 
a. Their axial ratio is .6830 : 1 : 1.1923 and composition Fe S As. 
Crystals of the third type are ie prismatic in the direction of ¢ and 
are bounded by the same are as are found in the second type. 
Their axial ratio is 6724: 1; 1.1896. Crystals from other localities 
show differences in pl eat and in axial ratio, and these differences 
are expressed in differences in habit. The formula best representing 
the composition of the mineral is thought to be Fe(S As), and varia- 
tions from ` are thought to be due to inclusions in the material anal- 
yzed. If Fe(As S), be considered the normal arsenopyrite ten per 
cent. of Fe S, may be replaced by Fe As, or the reverse, and the 
replacement will affect the axial ratio to a noticeable extent, an increase 
in Fe S, tending to increase the lengths of a and e. The substitution 
of Co and Ni for Fe affects the axes in the same way. an 
exhaustive article on the mineral deposits of Leogang in Salzburg, 
Buckrucker" gives a brief account of the region and a detailed descrip- ; 
tion of the many minerals occurring therein. Thirty-two distinct spe- : 
cies are referred to in the article, some briefly, others very extensively. | 
Among the latter are dolomite, aragonite, strontianite and celestite. 2 
E x, for aragonite is 30° 43.5. 2 V x, for strontianite is 6° í 59’ 12” 
“Ib, p. L 
MZeits. f. Kryst. xix, p. 113. 
