No.401.] REVIEWS OF RECENT LITERATURE. 453 
Among the applications of photography now being presented in 
The Process Photogram of London, that of recording tree forms, in 
the March number, is of interest to botanists, since, as the editor 
says, it is truly “a very difficult task to give a photographic account 
of a tree." 
PETROGRAPHY. 
The Petrographical Province of Essex County, Mass. — A very 
careful and critical study of the igneous rocks of Essex County, Mass., 
is given us by Washington! in a recent series of papers in the 
Journal of Geology. The district ‘is characterized as one of rocks 
which are more acid or more basic than normal, high in alkalis, 
with Na,O predominating over K,O, high in iron oxides, especially 
FeO, rather high in Al,O;, and low in MgO and CaO.” The rock 
types recognized are granites, quartz-syenites, diorites, essexites, 
gabbros, rhyolites, and the dike rocks, aplite, microgranite, diabase, 
paisanite, and camptonites. The essexites embrace also pulaskites 
and litchfieldites, characterized by the presence of albite, aes 
egirite, and alkaline amphiboles. 
All these rocks are regarded as differential phases of a laccolitic 
mass, with a composition approximating that of an acid diorite. 
The first differentiation of this magma is thought to have given 
rise to the granites, syenites, diorites, and the granito-diorite dikes, 
and a further local differentiation of the basic forms to foyaites, 
essexites, and paisanite-tinguaite dikes. 
Each of the rock types occurring in the district is carefully described, 
and of each a chemical analysis is given. The work is thorough. 
As the result of the paper, Essex County becomes one of the best 
known petrographical provinces in the country. 
he two most interesting dike rocks? of the district are a glauco- 
phane-sólvsbergite containing cordierite, and an analcite-tinguaite. 
Analyses of these two rocks follow: 
SiO. TiO, AlO, Fe,0, FeO MgO CaO NaO K,O H,O P,O; Ign. 
64-38 o 15.97 2.91 3.18 o  .85 7.28 | 5.07 08 ee 
56.75 JO »*éj 330 "(59 ud — 4)  :d4$ 490. C049 3. wi 99.92 
Nepheline-Syenites. — The corundum-bearing nepheline-syenites 
of Ontario are of such economic interest that the Canadian official 
V dots: of Geol., vol. vi, p. 787, uin in vii, pp. 53, 105, 284, and 465. 
. er. Journ. Sci., vol. vi, 1898, p 
