382 Tlie Aynerican Geologist. December, i898 
Golden Gate formation. 4. The San Pablo formation, which contains 
layers of rhyolytic tuff or pumice, of which two partial analyses are 
given. w. o. c. 
Syenite-porphyiy Dikes in the Northern Adirondacks. By H. P. 
Gushing. [Bull. Geo I. Soc. Am.,g, 2jg-2^6.) 
These dikes, of which fourteen have been discovered, and which are 
shown by their field relations to be younger than the pre-Cambrian 
gneisses and anorthosytes which constitute the mass of the Adiron- 
dacks, and older than the Potsdam sandstone, consist of a sub-acid, 
holocrystalline rock chiefly composed of acid feldspars (microperthite, 
albite, orthoclase and microcline) and biotite, with less abundant 
quartz and hornblende, and accessory magnetite, hematite, apatite and 
titanite, and various secondary species. Three original analyses are 
given, selected to represent the mean and extremes of composition; 
and from these the percentages of the component minerals are de- 
duced. In the discussion of the petrologic relationships of the dikes, 
numerous other analyses of the related rocks are quoted. w. o. c. 
Clay Deposits and Clay Industry in North Carolina. By Heinrich 
RiES. {North Carolina Geol. Surv., Bull, ij, 1-137.) 
Although regarded as a merely preliminary report, this is a fairly 
comprehensive, if not a detailed, account of the clays of a great state. 
But it is not of local interest only, for the admirable introductory 
sections, forming nearly half the work, and covering the chemical 
and physical properties, mining and preparation, of the clays is gen- 
eral, and more specifically of the kaolins or china clays, pottery 
clays, fire clays and brick clays, must prove of general interest and 
value. Under the chemical properties of clays are discussed: the 
iiuxing impurities, including the alkalies, compounds of iron, lime and 
magnesia; non-fluxing impurities, including silica titanium, organic 
matter and water; analytic methods; and the rational analysis of clays. 
The descriptive sections include nearly seventy original analysis of 
North Carolina clays by Prof. Chas. Baskerville of the State Univer- 
sity; and these are reported in tabular form at the end of the report. 
Each analysis gives the silica, alumina, ferric oxide, lime, magnesia, 
alkalies, moisture and water; and in certain cases the ferrous oxide, 
organic matter, sulphur and titanic oxide were also determined. By 
way of rational analyses, on which the value of a clay chiefly depends, 
the clay substance (pure kaolin), free and total fluxes are given in 
each case; and for the china clays also the percentages of quartz and 
feldspar in the sand. w. o. c. 
Weathering of A Inoyte in Manheim, New York. By C. H. Smyth, 
Jr. {Bull. Geol. Soc. Am., g, 237-268.) 
The alnoyte, which forms several small dikes in the Calciferous 
"sand rock" on East Canada creek, is an ultrabasic type, consisting 
largely of biotite and serpentine derived from the original olivine, the oli- 
vine itself being extremely rare; and the minor constituents are mag- 
