
1891.] Mineralogy and Fetrography. 827 
has, in many cases, given rise to thick accumulations of loose material, 
which has subsequently been used in the manufacture of the detrital beds. 
If the new beds were laid down under the influence of gentle currents 
their basal member would contain a large proportion of the material 
of the older rocks, and would thus simulate them to a greater or 
less extent. If this explanation is found to hold good, it will 
obviate the supposed necessity of regarding granite and gneiss as 
derived from fragmental rocks by some form of obscure metamor- 
phism. Rosenbusch ™ attacks the subject of the origin of the 
schists from a chemical standpoint. He shows by citing analyses that 
some foliated rocks have compositions corresponding to those of mas- 
sive rocks. These he regards as squeezed eruptives, Others are dif- 
ferent in composition from any known eruptive. These he regards as 
dynamically changed sedMMentaries. The foundation principle under- 
lying the argument is that dynamo-metamorphism affects but little 
chemical change in the material upon which it acts, except such as 
may be brought about by*percolating water. 

Mineralogical News.—The unique mineral me/anophlogite has 
been made the subject of recent study by Friedel ? and by Streng.! 
The former writer has examined the apparent cubes of the mineral in 
polarized light, and has found them to consist of six tetragonal pyra- 
mids, with their apices turned in and their bases forming the sides of 
the cubes. When heated the substance blackens and finally becomes 
opaque. Its density is 2.030—2.052, and the angle between contiguous 
cubic faces g1° 23’. The cubical cleavage reported by Lacroix does 
not exist. Some crystals appear to be simple cubes, while others are 
made up of many individuals, which in their section appear as fibers 
‘radiating from a center. They owe their form, consequently, not to 
pseudomorphism. They are pseudo-regular. A very careful analysis 
of these crystals yielded a result corresponding to 20SiO,+SO,, with 
small quantities of SrSO, and carbon. The crystals are implanted in 
opal. Other crystals, very similar to those described above, are the 
pseudomorphs of quartz described by Mallard. They have not the 
same density as melanophlogite, nor the same optical properties. 
The formation of the latter mineral is ascribed to the action of SO, on 
quartz. The author also describes fibrous crystals formed by the 
grouping of hexagonal lamelle with most of the properties of the 
u Miner. u. Petrog. Mitth., XIL., p. 49. 
12 Bull, Soc. Franc. d. Min., XIII., 1890, p. 356. 
13 Ber. d. Oberhess, Ges. f. Naturw. und Heilk, 1890, p. 114. Ref. Neues Jahrb. f. 
Min., etc., 1891, I., p. 18. ; 



