1897.) Mineralogy. 329 
The bombs are found strewn through the schists associated with the 
diabase. Their macroscopic features are carefully described with the 
aid of a number of figures. Some of the sheets are porphyritic with 
phenocrysts of irregularly outlined oligoclase surrounded by micas in 
a groundmass with the composition of normal diabase. The augite in 
this groundmass is sometimes idiomorphic, and in nearly all cases it is 
bordered by a rim of hornblende; often the hornblende replaces feld- 
spar laths embedded in the pyroxene, forming of them complete pseudo- 
morphs. The augite is replaced by calcite in some greens and by 
chlorite in others. 
The four structural types recognized by the author are: compact 
gabbroitic phases, compact ophitic varieties, compact porphyritic kinds 
and amygdaloidal varieties. The gabbroitic diabases are all gabbro- 
like in the land specimen. In thin section the feldspar grains break 
up into an aggregate of feldspar laths. The ophitic diabases present 
no unusual features except that in the coarse grained varieties the 
large feldspar grains are filled with inclusions of the other components. 
The amygdaloids are sometimes porphyritic, more frequently normal. 
On the contact between the diabase and the schists, both rocks have 
suffered from the effects of contact action. The diabase is much denser 
near the contact than at a greater distance from it, and in places is 
much altered, quartz being an abundant product of this alteration 
The schists, which are mainly roofing slates, are crystallized near their 
contact with the eruptives, 
MINERALOGY.’ 
The Production of Precious Stones in 1895. 
title Kunz’ reviews the chief features of the gem industry for the year, 
giving specially copious details concerning the American production. 
A six-carat diamond was found at Saukville, Wis., six miles from 
Milwaukee. In California several diamonds were found, one at Al- 
pine Creek, Tulare Co., five near Oroville, Butte Co., and about as 
many more from near the “head of the creek,” probably referring to 
one of the sources of the Feather River. From the association with 
peridotite, it seems probable that more may be found in this region. 
In South Africa the De Beers Company produced diamonds to the 
value of about $15,000,000 in the year ending July 1, 1895, and the 
| Edited by Prof. A. C. Gill, Cornell University, Ithaca, N. Y. 
* Seventeenth Annual Report of the U. S. Geol. Survey, 1896, pp. 895-926. 
