768 The American Naturalist. [September, 
Petrographical News.—Several banded inclusions from the 
tonalite of Mte. Aviole in the Tyrolese Alps have yielded Salomon*® 
some interesting observations. In one of the specimens one band is 
composed chiefly of hornblende so filled with elliptical inclusions of 
quartz, augite and glass that but a mere skeleton of the hornblendic 
material binds them together. A second band consists largely of 
augite. The third is principally an intergrowth of quartz and plag- 
ioclase in the form of a mosaic, whose particles are polygonal and 
straight edged. Specimens of contact rocks near the tonalite contain 
as accessory components sphene, biotite, quartz and zircon. The 
author calls attention to the peculiar cellular structure of the miner- 
als he describes and asserts that it is a characteristic structure for sub- 
stances formed by contact action. Aggregates of minerals exhibiting 
this ‘ contact structure’ he would call contact-amphibolites, contact- 
gneisses, etc., in accordance with their composition. In a note on 
the use of the gold washer’s pan as an instrument for the separation 
of the heavy constituents of sands and decomposed rocks Derby’ 
recounts his results of the examination of some granites and gneisses 
from the United States. In all the specimens examined there were 
found zircon grains, and these were especially plenty in granites from 
Otter Creek, Mt. Desert and the Hurricane Islands, in Maine, and 
from Ilchester, Md., and in the gneisses of Endfield, N. H., and Pas- 
coag, R. I. Monazite is particularly abundant in the granite of 
Westerly, R. I., and in the gneiss of Randolph, N. H. Xenotime was 
found in the gneiss of Wessford, Mass., and allanite, rutile and apatite 
in most of the rocks mentioned. The author thinks that there is a 
reasonable probability that zircon and monazite may prove to be 
guide minerals by which eruptive rocks may be detected, however 
much they may be disguised by metamorphism. The occurrence of 
these minerals in the crystalline schists is an indication that these 
rocks are squeezed eruptives and not changed sedimentaries. The 
conglomerate of Hoosac Mt., Mass., is overlain by an albite schist 
whose origin is ascribed by Wolff” largely to the replacement of clastic 
microline grains by albitic substance, with the attendant production of 
muscovite. Eight excellent figures in the author’s article show: the 
transition of decomposed fragments of feldspar into a fresh particle of 
albite in which all traces of clastic origin have disappeared. The 
*Neues. Jahrb. f. Min., etc., B. B, vii, p. 471. 
Proc. Rochester Acad. Sci., 1, 1891, p. 198. 
Bull. Mus. Comp. Zool., xvi, p. 173. 
