470 The American Naturalist. [May, 
for the determination of the common minerals from an examination of 
their physical properties. 
American mineralogists will look forward with interest to the text- 
book of mineralogy which is now in preparation for MacMillan & Co., 
by Mr. H. A. Miers, of the British Museum. 
W. H. Hosss. 
PETROGRAPHY.' 
Granite Inclusions in Gabbro.—Inclusions of granite in the 
gabbro of the Cuillin Hills, Skye, England, afford excellent illustra- 
tions of the effects produced by the fusion of acid rocks on a molten 
basic one. The granite in question is reported by Judd’ to be a biotite 
or a hornblende-biotite variety. Near the periphery of the mass the 
biotite and hornblende are replaced by augite, and granophyre is de- 
veloped in the interstices between the phenocrysts. The gabbro, in its 
passage upward, broke fragments from this granite, especially from its 
peripheral portions, and changed them completely. The granophyric 
intergrowth was fused and changed to a rhyolitic glass, marked by flow 
lines and filled with spherulites and lithophysae. In a few instances, 
some of the larger granophyre groups have escaped complete fusion, in 
which case, their remnants remain as nuclei of large compound spheru- 
lites. Imbedded in the glass are the large crystals of the granite. The 
quartzes have been cracked, and into the cracks glassy material has 
been pressed. The feldspars are also cracked, and in the crevices thus 
formed, secondary feldspars have been deposited. The original augites 
` have disappeared, and in their places are aggregates of magnetite and 
other secondary products. The most interesting features of the altered 
inclusions are the spherulites. Simple and composite varieties are both 
common, and the trichitic kinds described by Cross are also met with. 
The centers of the spherulites are nearly always grains of quartz or 
of orthoclase, or groups of granophyre, as already mentioned. Pyrite 
and fayalite are both new products of the metamorphic action. 
The Geology of Pretoria, South Africa.—A long and inter- 
_ esting account of the geology of the gold fields near Pretoria, in the 
1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Maine. 
* Quart. Jour. Geol. Soc., xlix, p. 175. 
