452 General Notes. 
Alps; (b) that which occurred during the glacial period; (c) that 
which is the work of the modern epoch. 
Four years ago M. G. Rolland announced his belief that the 
great fresh-water formations of the Sahara are much less recent 
than had been hitherto believed, the greater portion of them 
belonging to the pliocene instead of the quaternary age. Subse- 
quent studies of these deposits have confirmed his first opinion, of 
which he las now found paleontological proof by the discovery 
of a number of casts of species of Helix belonging to the group of 
H. tissoti and semperina, which characterize the lower pliocene of 
Biskra and Constantine. M. Rolland also shows the synchronism 
which exists between the different beds of the Eastern Sahara and 
the corresponding fresh-water beds of the pliocene and quaternary 
formations in the Atlas region. 
MINERALOGY AND PETROGRAPHY.' 
PETROGRAPHICAL NeEws.—Among the rocks gathered by 
Reyer? during a journey through the Sierra Nevada Mountains, 
Schuster* has found the following principal types: biotite granites, 
containing microcline and _pilitized biotite; saussurite-diorite and 
quartz-diorite, containing orthoclase ; saussurite, pilite, and biotite 
gabbros ; quartz-porphyrites, kersantites, andesites, serpentine, frag- 
mental rocks, and tufas. Although the paper in which these rocks 
are described consists merely of detailed descriptions of detached 
rock-specimens, it nevertheless contains many points of considerable 
interest. Pyrophyllite is mentioned as an alteration product 0 
olivine and of plagioclase; reaction rims around augite and olivine 
are pictured; intergrowths of biotite and augite, of biotite and 
hornblende, and the alteration of biotite into pilite and into horn- 
blende, are each described. romium mica is mentioned as occur- 
ring in a magnesite concretion in serpentine ; helminth, as a constit- 
uent of a diabase porphyrite, and anorthoclase, as existing 10 4 © 
hornblende porphyrite. A most interesting case of intergrowth 1s 
that in which a long, tabular crystal of plagioclase penetrates dial- 
lage in sucha way that its long edges are parallel to the orthopinacoid 
of the augite, and its twining lamelle are parallel to the lines of 
inclusions in this mineral. Indications of the effects of pressure 
were seen in a large number of the sections examined.——V!- 
Wadsworth‘ has recently published a report embracing preliminary 
descriptions of the peridotites, gabbros, diabases, and other rocks of 
1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Me. 
s Neues bes Prag etc. Beil. Bd. v., p. 451. 
: ati us Nat. ist. Survey of Minnesota, Bulletin No. 2. Minne- 
apolis, 1887. ; 
