274 PETROLOGICAL ABSTRACTS AND REVIEWS 
of the other rocks are recalculated by dividing their A, C, and F values 
by the same values in the average rock. The new values are indicated 
by A; Cz and Fy, and are called ‘“‘topical” parameters. As recalculated, 
the plutonic rocks lie equally distributed in each quadrant of the figure. 
Osann, A., and Ummauer, O. ‘Uber einen Osannithornblendit, 
ein feldspathfreies Endglied der Alkalireihe von Alter Pedroso,” 
Sitzb. Heidelberger Akad. Wiss., Math.-naturw. Kl., 1914, A 16, 
pp. 10, pls. 2, bibliography, analyses. 
Description of narrow, black dikes occurring in a light-colored 
alkali-syenite in Portugal. The rock consists entirely of amphibole 
(osannite) with a little magnetite; light-colored constituents, biotite, 
and pyroxene are entirely wanting. 
PatMeER, Harotp S. ‘‘Geological Notes on the Andes of North- 
western Argentina,” Amer. Jour. Sci., XXXVIII (1914), 309- 
BOM eS a0: 
This paper gives the results of a reconnaissance trip from Salta, . 
Argentina, to Calama, Chile. The author finds evidence of the deposi- 
tion of Paleozoic sediments, their later metamorphism during or following 
the intrusion of granite and granite-porphyry, subsequent erosion, depo- 
sition of Jurassic sediments, a period of vertical movements which 
folded and faulted the rocks, and a period of great volcanic activity, 
beginning in the Tertiary and continuing till recent times, during which 
rhyolites and andesites were erupted. There is evidence of some 
glaciation in the Eastern Cordillera. 
Pirsson, L. V. “The Microscopical Characters of Volcanic Tufis 
—A Study for Students,” Amer. Jour. Sci., XL (1915), 191- 
2a Sane 
The author points out the difficulty in determining the tuffs when 
they have become altered by weathering, by burial under later sediments, 
or by metamorphism, and the difficulty in determining whether such 
rocks are igneous or sedimentary. No systematic or adequate treat- 
ment of the tuffs being given in petrographic textbooks, he tells his 
own experience in studying them. 
Fragmental volcanic material is classified, according to the size of 
the material, into bombs, lapilli, ashes, and dust. The coarser material 
