1895.] - | Petrography. 43 
bros include olivinitic and non-olivinitic varieties. In the former there 
is often a bluish-green hornblende, at whose contact with feldspar there 
is often a fringe of spinel arranged in pseudopodia-like masses with 
their long directions perpendicular to the bounding surfaces of the 
amphibole. In other specimens the olivine is separated from feldspar 
by a band of hypersthene. Norites, with reaction-rims around their 
olivines, and peridotites containing enstatite are among the other mem- 
bers of the gabbro family met with. More closely associated with the 
schists than all the rocks just mentioned, and apparently forming a 
portion of the schist series, are diorites, often saussuritized, and amphi- 
bolites among the hornblende rocks, and gabbros, peridotites and ser- 
pentines among the pyroxene bearing kinds. The basic schistose rocks. 
in the collection studied are schistose diorites, and rocks com posed essen- 
tially of epidote and zoisite, and of garnet and scapolite, supposed to 
be derived from diorite, schistose gabbros and hornblende schists. 
After describing the characteristic features of the gabbro and diorite 
structures, the author proceeds to discuss the origin of the Argentine 
hornblende schists. He finds no evidence that these are squeezed plu- 
tonic rocks nor metamorphosed sediments, and so he concludes that. 
they are submarine eruptives. 
Amphiboles in Russian Rocks.—Federow’ gives some interest- 
ing notes on the amphiboles in the rocks‘of the northern Urals. The 
mineral is frequently absent from the freshest rocks. It is most abun- 
dantly present in those that have been metamorphosed by pressure. 
The kinds observed were a yellow-green variety, a colorless or very 
light colored kind, a dark brown variety, a fibrous variety with a blue 
color, glaucophane and gastaldite. The first is especially common in 
gneiss, syenite and syenitic gneiss, and it is present also in a diabase, 
where it is believed to have been derived from chlorite. The second 
variety is common to highly metamorphic rocks, while the third is lim- 
ited to diabases and proterobases. The fourth variety is characteristic 
of the green schists, more particularly those that have undergone 
chemical alterations. The glaucophane is found in magnetite schists, 
in a few altered green schists and in gneiss. The sixth variety is also 
common to the green schists. In a syenite gneiss the author observed 
a brown augite that along a zone of crushing has been changed to a 
light green pyroxene, which is regarded as evidence that dark brown 
amphibole may give rise by pressure to light green hornblende. 
6 Minn. u. Petrog. Mitth., xiv, p. 143. 
