844 lievieiv of liecent Geological Literature. 
ending with the triclinic. This is followed by some tables of hardness and 
specific gravity and of optical constants of the principal rock-forming 
minerals. For the beginner this is the best book we have seen in the 
English language, and it will serve well as a reference book for those 
more advanced. 
In the annals of the New York Academy of Si-iencca, vol. i\, (July, 1888,) 
is the conclusion of Prof. A. A. Julien's investigation into the cause of the 
variation of the rate of decomposition of iron jiyrites, and its relation to 
density. One hundred and fifteen samples were subjected to careful ex- 
amination. These were derived from different parts of America and Europe. 
After mentioning numerous hypothetical explanations of this variation, 
advanced by mineralogists, he gives the results of the chemical analysis of 
a specimen'of spear-headed marcasite from the chalk of Folkestone,England 
and of another of fibrous, white and brilliant pyrite from near Galena, 111. 
The nearness of the actual to the theoretical constitution of pyrite in each 
case, he considers demonstrative of the absence of all iron proto-sulphide 
the presence of which had been suggested by Berzelius as the cause of 
rapid decomposition, through the easy formation of the proto-sulphate, and 
which has been received generally as the true cause. 
He also further concludes that "difference of chemical composition has 
nothing to do with the differing quickness of tendency to decomposition," 
and that its cause must be sought in some other direction. 
By means of microscopical examination by reflected light, the minute 
difference of the natural surface was observed in different ways, in a num- 
ber of samples. Here were noted the following characters: Fineness of 
grain, distortion of aggregated cubes, concentric lines of growth, staining 
by tarnish and by efflorescence, and its distribution over the different parts, 
staining to brownish-black and the depth to which it penetrates, fissures 
and finer lineation, internal cleavage, the crystals of the efflorescing salt, 
&c. From the observations made, which are given in detail in the Jour. 
N. Y. Mic. Soc. (1886) 1-12, Prof . Julien concludes : (1) In the fibrous 
nodules of pyrites, the outward growth of the elongated cubes, of which 
the fibers consist, and their mutual compression, have produced a condition 
of great tension, which has facilitated the later disintegration. (2) The 
material is mainly composed of a diluted mixture of pyrite with a paler 
colored andimstable impurity. Through this mixture more or less pure 
pyrite is diffused in alternating films or in scattered strings and crystals of 
a deeper yellow color than that of their matrix. (3) The oxidation of the 
material has been facilitated by its heterogeneous composition, by its 
fissured structure, and by the tension among its fibers. It has progressed 
more rapidly in the predominant parti-colored mixture, has penetrated 
along the seams between the fibers, and has then been hastened by the 
development of the more minute Assuring, as the result of the tension. (4) 
The development of this system of minute fissures has furnished an enor- 
mous area for the internal condensation of gases and vapors from the 
atmosphere, chiefly oxygen and moisture, which has resulted in the speedy 
oxidation, pitting, decay, production of crystals of vitriol, expansion and 
final disintegration observed in such forms of pyrites. (5) The mode of 
