602 The American Naturalist. [July, 
are squeezed eruptives, and discusses the physical, mineralogical and 
chemical changes that have effected the alteration of the granites and 
diorites into gneisses and schists of various kinds. His conclusion 
that a sericite schist may be derived from diorite and that biotite is 
often an alteration product of chlorite are both of great interest. In 
the change of a massive into a schistise rock, the author states that the 
former “ passes through the intermediate state of a laminated grit, 
which thus simulates a true sediment, the subsequent stages of alter- 
ation and cementation resembling the process of metamorphism in 
some bedded rocks.” In the production of the foliation there is de- 
composition of the original components of the massive rock and a re- 
construction of new, minerals largely from these decomposition pro- 
ducts. In the Malvern Hill rocks orthoclase has been replaced by 
quartz and muscovite, plagioclase by quartz and muscovite, chlorite by 
biotite and white mica, and biotite by a white mica. A number of 
analyses appear in the paper to illustrate the chemical changes that 
have accompanied the physical ones through which the respective 
rocks have passed, 
A Soda-Rhyolite from the Berkeley Hills, Cal.—In the 
Contra Costa Hills near Berkeley, California, are occurrences of a 
voleanie flow that has been investigated by Palache, who recognizes 
three facies of the rock. In the first, the porphyritic phase, pheno- 
erysts of quartz and feldspar are abundantly disseminated through a 
micro-grauular aggregate of the same minerals. The second phase is 
characterized by the possession of numerous small spherulites in a 
glassy matrix, in which are a few small grains of magnetite and some 
feathery aggregates of chaleedony. The third phase is a glass con- 
taining tiny microlites of feldspar and grains of magnetite. Analyses 
of the different types indicate that the material of each type has the 
composition of a soda-rhyolite. The spherulitic variety which is inter- 
mediate between the other two, in its acidity is composed as follows: 
SiO, ALO, ar CaO MgO K,O Na,O H,O Total Density 
75.46 13.18 95 .10 1.09 688 .93 = 99.50 2.42 
Diabases from Rio Janeiro, Brazil.—Sections from a series of 
twelve diabase dykes from Rio Janeiro, Brazil, have been investigated 
by Hovey,’ with some interesting results. The chemical composition 
*Bull. Dept. Geol. Univ, Cal., Vol. 1, p. 61. 
5Min. u. Petrog, Mitth. XIII, p. 211, 
