772 Ihe American Naturalist. [August, . 
A recent study of the corresponding series of beds in the Paris 
and Hempstead basins leads Mr. A. Blytt to think that the attenua- 
tion of strata was effected by a general cause, and it seems highly 
probable that this cause is the precession of the equinoxes. 
In the Proc. N. Y. Microscopical Soc., 1890, is found a synopsis of 
thé Cretaceous Foraminifera of New Jersey, compiled by Anthony 
Woodward. The object of this paper is to bring together all the 
work that has been previously done, and the observations that have 
been made on the Cretaceous Foraminifera of New Jersey from 1833 
to 1889. 
Joseph Moore (Jour. Cin. Soc. Nat. His., April, 1890) describes 
the tooth of a gigantic rodent found in northern Georgia, Its striking 
feature is the peculiar ribbing and flutting of the enamel through- 
out the length of the tooth. He proposes the name Castoroides geor- 
gemis. After an examination of the specimen, Prof. Cope states that 
it is the inferior canine of the Hippopotamus amphibius. 
MINERALOGY AND PETROGRAPHY.! 
Petrographical News.—A suite of rocks collected in Madagas- 
car by Rev. R. Baron? has been examined by Hatch,? who separates. 
them into gneisses, granitite, olivine-norite, pyroxene-granulites, 
pyroxenites, and basalts. In the olivine-norite the plagioclase is per- 
fectly transparent, and has an undulous extinction. The olivine is 
surrounded by a reactionary rim consisting of an inner zone of hypers- 
thene and an outer one of actinolite. The pyroxene-granulite is 
evidently a basic eruptive that has suffered dynamo-metamorphism. It 
contains pyroxent, hornblende, and garnet, besides the usual constit- 
uents of granulite. Among the basalts many varieties are described. 
In one variety, the augite and olivine, when present, are in porphyritic 
crystals, slightly corroded, and including portions of the microlitic 
ground mass. The augite is grouped around the olivine, which is 
twinned. A few grains of quartz are present. A second variety con- 
tains hornblende and biotite porphyritically developed. All the 
augite of this rock is zonal, with a different extinction in the various 
zones. In some the hour-glass structure was observed. Twinning is 
frequent. A glassy basalt includes hornblende crystals and fragments 
uartz. Some of the hornblende has been entirely dissolved, and 
in its place has been formed an aggregate of augite and magnetite. 
! Edited by Dr. W. S. Bayley, Colby ae e Waterville, Me. 
? Quart. Jour. Geol. Soc., XLV., May, 1889; p. 
