Review of Recent Geological Literature. 381 
Chemical and Mineral Relationships in Igneous Rocks. By Joseph 
P. Iddings. (/. Geol.,6, 2ig-2jy.) 
This is an attempt to correlate the mineral composition of igneous 
rocks with the chemical composition of their magmas; that is, of each 
rock as a whole. The chief difificulties are: first, the variable composi- 
tion of the rock making minerals, quartz alone having an absolutely 
fixed composition, and no element occurring only in one mineral; sec- 
ond, the fact that no fixed association of minerals necessarily results 
from the crystallization of a magma, the result being largely con- 
trolled by the physical conditions. To avoid undue complexity, the 
author confines his attention to the more important rock-making 
minerals, including quartz, feldspathic minerals, micas, pyroxenes, 
amphiboles, olivine and magnetite. The empirical and dualistic for- 
mulas are given for each species; and the latter are classified in ac- 
cordance with the ratios of the protoxide and sesquioxide bases to the 
silica. After quoting briefly some of the laws governing the rela- 
tions of the mineral and chemical composition formulated in an earlier 
paper, the author discusses in greater detail and with the aid of dia- 
grams, the relations particularly of quartz, and of leucite, nephelite 
and sodalite, thus making more evident the interdependence of the 
various minerals on one another and on the chemical composition 
of the magma. w. o. c. 
A Study of some Examples of Rock Variation. By J. Morgan 
Clements. {J. Geol.,6, jy2-jg2.) 
The rocks in question include diorytes, gabbros, norytes and peri- 
dotytes occurring in the Crystal Falls iron-bearing district of Michi- 
gan. Petrographic descriptions and chemical analyses of the several 
types are followed by discussion of their chemical relations, the com- 
plete analyses, percentages of the chief oxides, and atomic propor- 
tions of the metals being presented in tabular form, and the author 
concludes that the rapid changes in mineralogical composition and 
texture in a single rock exposure, and the changes thus occasioned 
from one rock into another through intermediate facies show very 
clearly the intimate relationship of the rocks to one another, and war- 
rants the assumption that they all belong to a geological unit. 
w. o. c. 
Notes on some Igneous, Mctamorphic and Sedimentary Rocks of the 
Coast Ranges of California. By H. W. Tuunek. (/. Geol.. 6, ./8j-./gg.) 
The rocks considered in this paper include: i. Metabasalts and 
diabases, formerly regarded as metamorphic sandstones, of which ten 
analyses are quoted without discussion. 2. Serpentine, which has also 
been regarded as, in part at least, altered sedimentary rocks, but which 
the author holds to be, in the main, at least, of igneous origin. Nine 
analyses, representing five localities are quoted, showing great uni- 
formity of composition and indicating that olivine or rhombic pyrox- 
ene must have been a prominent constituent of all of the original 
rocks from which the serpentines were derived. 3. The Franciscan or 
