PETROLOGICAL ABSTRACTS AND REVIEWS 381 
broken up and intruded by later material. Locally there is a more basic 
phase where the magma differentiated against the slate or even under 
its own. cover, and the rock is rhombic porphyry. No complementary 
dikes occur in the region. 
WarREN, CHartEsSH. “A Quantitative Study of Certain Perthitic 
Feldspars,”’ Proc. Amer. Acad. Arts and Sci., LI (1915), 127- 
SA. OVER Ae 
Micrometric readings and calculations from analyses of eight per- 
thites show microcline 52.3-86.2 to albite 47.7-13.8 per cent by 
weight. The author comes to the conclusion held by Vogt, that per- 
thitic structure in primary potassic feldspar, where the amount of albite 
is less than ca. 28 per cent, is due to the unmixing of previously homo- 
geneous mixed crystals. 
WARREN, CHARLES H., and Powers, SmNEY. ‘Geology of 
the Diamond Hill-Cumberland District in Rhode Island— 
Massachusetts,” Bull. Geol. Soc. Amer., XXV (1915), 435-76, 
figs. 3. 
Gives a geological history of the region, and describes gabbro, 
cumberlandite, serpentine, labradorite-porphyry, quartz-diorite, granite, 
riebeckite-aegirite-granite, felsite, and various porphyries. 
WASHINGTON, HENRY S. “The Volcanic Cycles in Sardinia.” 
Cong. géol. internat. Canada, 1913. Pp. 11. 
A preliminary statement of some of the general petrological relation- 
ships of the igneous rocks of Sardinia, and the bearing of these on certain 
phases of magmatic differentiation. 
WASHINGTON, HENRY S., and Larsen, E. S. ‘‘Magnetite basalt 
from North Park, Colorado,” Jour. Wash. Acad. Sc., II 
(1913), 449-52, analysis. 
A brief description of a peculiar basalt from Colorado which contains 
55 per cent of iron ore. It is the only known example of extruded lava 
so high in iron. 
