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Mineralogy and Petrography. 61 
are wooded, and slope gently. Dr. Jhering’s map (Petermann’s Mit- 
teilungen) shows that the Cainacuam has five mouths, while that 
of the government engineer (1882) shows but three. Many valu- 
able woods occur in the forests. The “campos,” or open tracts, 
which are invariably higher than the forest-covered country, are 
referred by Dr. Jhering to the diluvial period, while the wooded 
lands are alluvial. 
M. von Fetvelde, in a “Notice” upon the Congo Free State, 
gives its area at 1,075,000 square miles. 
MINERALOGY AND PETROGRAPHY:.' 
PETROGRAPHICAL NEws.—The volcanic bombs from the Lake 
Laach district are divided by Hubbard? into four classes—old 
crystalline and schistose bombs, sanidinite bombs, trachyte bombs, 
and basalt bombs. The last three varieties are difficult to separate 
from each other, but are easily distinguishable from the first class. 
After discussing very briefly the various theories proposed to account 
for these bodies, the author proceeds to investigate those in which 
nosean occurs. He examines two hundred and sixty thin sections 
of nosean-bearing bombs, and reaches the following conclusions : 
(1.) The Nosean is in greater part a druse mineral. (2.) The inclus- 
sion so characteristic of this mineral consist of magnetite, either fresh 
or slightly altered. (3.) The little red octahedra so frequently accom- 
panying the titanite of the Lake Laach bombs is closely related to 
the pyrrhite of San Miguel, and has probably been derived by the 
alteration of titanite. Several other points of interest in relation to 
the minerals occurring in these bombs are noted. The most impor- 
tant results reached, however, are those which have been mentioned. 
—The elzeolite-syenite from the vicinity of Rio de Janeiro, Brazil, 
has recently been carefully examined by Fr. Graeff? The mass o 
the rock is described as possessing a holocrystalline hypidiomor- 
phic structure. Its principal constituents are hornblende, ortho- 
clase, eleeolite, augite, and mica. The feldspar is noticeable for the 
possession of a parting‘ parallel to 7 Pæ. In other cases it is 
intergrown with very fine lamellz of plagioclase, thus showing stri- 
ations when examined under the microscope in polarized light. The 
elæolite is generally fresh, but in some instances is altered 
into sodalite and analcite. The accessory minerals are titanite, 
apatite, zircon, fluorite and a black garnet. The rock is interesting, 
as affording another example of the predominance of hornblende 
p edited by Dr. W. S. Bayley, Madison, Wisconsin. 
k pieh u. Petrog. Mitth., viii., 1887, p. 356. 
i s Jahrb. f. Min., ete., 1887, ii. p. 222. 
cf. W. Cross, Monog. xii. U. S. Geol. Survey, p. 348. Mr. Cross finds 
paag in the sanidine of the Leadville rhyolites, which is parallel to 
Oe 
