FPETROLOGICAL ABSTRACTS AND REVIEWS 
LOEWINSON-LESSING, FRANZ. ‘‘The Fundamental Problems of 
Petrogenesis, or the Origin of Igneous Rocks,” Geol. Mag., 
N.S., Dec. V, VIII (1911), 248-57, 280-97. 
HARKER, ALFRED. “Some Aspects of Modern Petrology,’ Vice- 
presidential address before Section C of the British Assoc. 
Adv. sci Portsmouth, 1911. Ep 12. 
IppIncs, JosEPH P. ‘‘Problems in Petrology,” Proc. Amer. Phil. 
Soc., L. (1911), 286-300. 
Cross, Wuitman. “‘The Natural Classification of Igneous 
Rocks,” Quar. Jour. Geol. Soc. (of London), LXVI (1910), 
470-506. 
Discussion of the great problems of igneous rocks is a necessary 
forerunner of any unanimity of belief concerning them, such as must 
exist before the science of petrology can claim to have advanced beyond 
the formulative stages. In the papers here under review many of these 
problems are freely discussed from different standpoints. An outline of 
their scope and character may serve to show the present condition of the 
science of petrology. 
The problems of petrogenesis discussed by Loewinson-Lessing are 
indeed fundamental, some of them reaching so far back into the earth’s 
history or dealing with phenomena of such depths in its mass that few 
petrologists speak with confidence of their solution upon our present 
meager basis of established fact. The author of the essay under review 
is one of those who do speak with an assurance for which there is scant 
justification in the considerations presented, or, indeed, in the knowledge 
of today. Yet such discussions are of undoubted interest and value in 
more ways than one. 
Loewinson-Lessing believes in two primordial magmas which he calls 
granitic and gabbroidal. He advocates, as he acknowledges, the ideas 
of Bunsen and Michel-Lévy in modified form. It is sought to establish 
the primordial nature of these two magmas by discussing the average 
composition of the earth’s crust. The known variations exhibited by 
igneous rocks are ascribed to differentiation, assimilation, and, in appar- 
ently subordinate degree, to mixture of the two original magmas. 
In discussion of ‘‘the average chemical composition of the earth’s 
362 
