386 The American Naturalist. [April, 
this phenomenon and has carefully examined a number of the mem- 
bers of the group with a view to learning something of the changes 
effected in them by the loss of water. Natrolite appears monoclinic 
under these conditions, scolecite orthorhombic, stilbite orthorhombic, 
and each of the other zeolites affords a corresponding meta-zeolite. 
The optical anomalies often observed in these minerals is thought to be 
undoubtedly due to partial loss of water. 
Isomorphism.—<After a long mathematical discussion of the 
theory of the structure of isomorphous mixtures and upon compari- 
son of the results of investigations upon the optical properties of 
mixed crystals, Poeckel™ concludes that we have not yet sufficient 
data to decide as to whether Mallard’s lamellz theory of the constitu- 
tion of these bodies is correct or not. 
By the use of the method” in which colored and colorless crystals 
of supposed isomorphous substances are allowed to form under the 
microscope Retgers™ has proven that the alkaline ferrates are isomor- 
phous with the corresponding sulphates, selenates, molybdates and 
tungstates, that the potassium tellurates and osmiates are isodimor- 
phous, and that the rutheniate of this metal is isomorphous with its 
uranate. 
The arguments for and against the view as to the isomorphism of 
calcite and dolomite are given respectively by Brauns and Retgers” 
in a recent letter to the Neues, Jahrbuch. The discussion is too 
involved to warrant an intelligible abstract in these notes. 
Etched Figures.—The matrix of the African diamonds is capable 
of resorbing” diamonds, producing on their faces irregular, long, and 
hemispherical hollows, associated with which are little spheres and 
grains of black carbonaceous substance, supposed to be a compound of 
iron and carbon. 
Hofer” describes corrosian forms on the calcites of Steierdorf, Banat, 
and of Rauris and Salzburg, and ascribes the hexoctahedral faces 
*#02 on the fluorite of Sarnthal, Tyrol, to corrosive processes. 
™Neues. Jahrb. f. Min., etc.,-B. B., viii, 1892, p. 117. 
AMERICAN NATURALIST, June, 1892, p. 517. 
*Zeits. f. Physik. Chem., x, 5, 1892, p. 529. 
Neues. Jahrb. f. Min., etc., 1892, II, p. 210. 
%Ber. deutsch. chem. Ges., 1892, p. 2470. 
"Min. u. Petrog., Mitth. xii, p. 487. 
