Reviezu of Recent Geological Literature. 255 
well as of water and carbonaceous matter. The most noteworthy 
contrast between the clay slate and the contact rocks is shown in the 
relations of potash and soda. For the clay slate the percentages are 
5.73 and 0.54, respectively, while in the contact rocks these proportions 
are reversed, the successive values for potash being 0.70, 0.22, 0.15. and 
for soda 6.72, 8.22, 6.57. This agrees with the fact that, while albite is 
wanting in the clay slate, it is an abundant constituent of the contact 
rocks. The author concludes that the changes in ultimate chemical 
composition are probably best explained as due to an actual transfer 
of material, possibly in the form of a soda silicate, from the basic 
igneous rock to the intruded slate. w. o. c. 
The Petrograpical Province of Essex County, Mass. By Henry 
S. Washington. (J. Geol., 6, 787-808; 7, 5364, 105-121. 284-294.) 
Although Essex county is a region of great petrographic diversity 
and interest, and its rocks have received much attention from geolo- 
gists in the past, and are the subject of a considerable literature, this 
series of papers is the first systematic and comprehensive petrological 
study of this now classic area. The author confines his attention to 
the igneous rocks, which include chiefly granites, ciuartz-syenytes, 
syenytes, nepheline-syenytes, essexytes, diorytes, and gabbros, cut by 
numerous dikes and with later flows of rhyolyte. The entire series 
is regarded as pre-Carboniferous and post-Cambrian, having cut and 
metamorphosed the Cam.brian strata of the region. The descriptions 
'are supplemented by chemical analyses and a general discussion of 
the results, including a comparison of this region with others of 
similar character. The granites are all hornblendic, but contain also 
more or less glaucophane and biotite, and the accessories include 
danalite, fayalite, allanite, epidote, zircon, magnetite, apatite, fluorite. 
Th^e feldspar is all of the most acid alkali varieties, including ortho- 
clase, microcline, and albite, occurring largely as highly typical micro- 
perthites and cryptoperthites. The analysis shows a typical acid gran- 
ite, rich in potash and low in lime and iron oxides. The mineralogical 
composition, as for most of the rocks studied, is calculated from the 
analysis. Included masses of darker color and finer grain are found 
to consist of the same essential minerals as the granite, but in differ- 
ent proportions, analysis showing 10 per cent, less silica and much 
more iron oxide, corresponding to a quartz-syenyte. Alkenyte, or au- 
gitic quartz-syenyte is found to be almost as abundant as the granites, 
and the analysis shows it to be closely similar in composition to the 
dark inclusions of the granite, and like these it is regarded as a differ- 
entiation of the granite magma. Another very slight differentiation is 
afforded by the nordmarkyte or mica-hornblende-quartz-syenyte, and 
the more acid character of this type finds mineralogical expression in 
the substitution of biotite and hornblende for augite. More strongly 
contrasted with these, and with an unquestionable claim to separate 
recognition is the nepheline syenyte, which has, in comparison, a 
rather limited development. Two main structure types are recognized, 
a granitic and a trachytic, which shade into each other and corre- 
