278 PETROLOGICAL ABSTRACTS AND REVIEWS 
Rocers, AusTIn F. “A New Specific Gravity Balance,” Science, 
XXXIV (1011), 58-60. 
This is a modification of the ordinary beam balance by which the 
specific gravity is read off directly from the beam. The graduations on 
the beam are the results of calculations for the various densities. The 
graduation is in units from 2 to Io, in tenths from 2 to 4, in fifths from 
5 to 6, and in halves from 6 to 10. For such minerals as quartz, using 
a mass of two or three grams, the balance is accurate to about two units 
in the second decimal place. 
HAROLD E. CULVER 
~Rocers, G. S. ‘The Geology of the Cortlandt Series and Its 
Emery Deposits,’ Annals, N.Y. Acad. Sci., XXI (1911), 
Tr OO: 
The Cortlandt series, best known perhaps through the classic 
researches of George H. Williams, covers about thirty square miles just 
southeast of Peekskill, N.Y., on the Hudson River. The following 
rocks, the distribution of which is shown on a colored map, constitute the 
principal types, although many of them grade into one another; granite, 
syenite, sodalite syenite, diorite, gabbro, hornblendite, biotite norite, 
augite norite, biotite augite norite, hornblende norite, biotite horn- 
blende norite, olivine norite, quartz norite, pyroxenite, hornblende 
pyroxenite, olivine pyroxenite, biotite peridotite, and many dike rocks. 
Complete petrographic descriptions are given, together with seventeen 
new analyses. Surrounding the series is the Manhattan schist, associated 
with the Fordham gneiss and Inwood limestone, and xenoliths of these 
rocks are found in the series itself. The latter is therefore younger, but 
is older than the Triassic shales across the river, and is probably late 
Paleozoic. In general, no metamorphism is found in the series, but an 
original gneissoid structure is common; and from the evidence afforded 
therein, as well as from the distribution of the types, it is thought that 
the pyroxenite group was extruded first, followed closely by the norites, 
with the granites distinctly later. The position of the diorite group is 
problematical; it is possible that these types are the product of reactions 
between the igneous rocks and the surrounding metamorphics. 
It is found that contact action between the igneous rocks and the 
limestone give rise to abnormal wernerite, tremolite, and grossularite 
mixtures; and similarly, contact with the aluminous schist produces a 
concentration of the biotite and magnetite of the latter, with the fre- 
quent formation of almandite, sillimanite, spinel, corundum, etc. The 
