946 The American Naturalist. [November, 
General Notes. 
p 
PETROGRAPHY. 
Zirkel's Petrographie.—The second volume of Zirkel's treatise 
on Petrography? has recently appeared in America. It treats with 
such fulness of the massive rocks that an epitome of its contents is out 
of the question in this place. The volume discusses the composition, 
mineral and chemical, the structure and the distribution of the various 
types of the eruptive rocks with a thoroughness found only in German 
text-books. The descriptions of their important occurrences will be 
especially valuable to the student who has not a library at his disposal ; 
and to the investigator, the large and accurate lists of references scat- 
tered through the book are very welcome, Many petrographers will 
differ with the author as to the importance and desirability of some of 
his types, and others will find fault with him concerning some of histhe- 
ories, as, for instance, that of the origin of olivine aggregates in basalts. 
'The volume is, however, on the whole quite free from theoretical dis- 
cussions. While it loses something of its interest in consequence of 
this lack of theory, the book gains the confidence of the reader, who 
desires more particularly an account of the work done in the different 
provinces, where the rocks in which he is interested are to be found. 
Inclusions in Volcanic Rocks.—T wo articles on the petrograph- 
ical changes affected by the partial or entire solution of foreign inclu- 
sions in voleanic rocks have recently appeared. The first is an essay 
by Dannenberg, and the second a volume of 710 pages by Lacroix.* 
Dannenbergs í article pena more particulari of the inclusions in the 
l trachytes. Zircons, corundum, mag- 
netite, pyrite, feldspar. sillimanite, quartz, sandstone, schists and gran- 
ite were found included in both basic and acid rocks of the region. 
Those inclusions that were most similar to the including rocks suffered 
much less alteration than those that differed most in chemical compo- 
sition from the lavas. The aluminous compounds frequently yielded 
IEdited by Dr. W. S. Bayley, Colby University, Waterville, Me. 
2F, Zirkel: Lehrbuch der oo Leipzig, 1894, pp. iv and 941. 
?Min. u. Petrog. Mitth. XIV, 
*Les Enclaves des Roches poda Macon, 1898, pp. 710, pl. vii, fig. 84. 
SERO VERRE NUN RIT T ERE NIE TT a ET 
