bo 
~J 
by 
The American Naturalist. [March, 
MINERALOGY AND PETROGRAPHY:' 
The Rocks of the Thalhorn.—In the Thalhorn of the Upper 
Amariner Thal are found a porphyritic granite, between conglomerates 
composed of gabbro pebbles in a schistose matrix, and also serpen- 
tines, massive gabbro, schists, and various contact rocks. Linck? gives 
a good petrographical description of all these, and geological notes of 
their occurrence. e main granite mass is a portion of the well- 
known Kamm granite. It is found in dykes and flows, and it varies 
in its composition and structure from a typical granitite containing 
two feldspars, through porphyritic granite and syenite to lamprophyric 
minettes. The unaltered sediments near the eruptive are graywackes. 
On the contact with the granite the clastics are altered to knotty schists 
that are predominantly biotite schists flecked with light spots, consist- 
ing mainly of quartz and feldspar in micropegmatitic intergrowths, 
surrounded by biotite. Extreme alteration gives rise to hornstones, of 
which the writer recognizes several varieties. In these biotite, feld- 
spar, hornblende and micropegmatite are so orientated as to resemble 
the poicilitic structure of many diabases and other basic rocks. Horn- 
blende is abundant in them as needles scattered through the ground- 
mass and as large phenocrysts. The conglomerates occupy the greater 
share of the writer’s attention. In one group acid pebbles occur in 4 
sandy or clayey matrix of basic detritus, in which biotite, feldspar and 
hornblende are new products of alteration. A second group includes 
rocks made up partly of gabbro material. Here the author again 
recognizes two groups, in one of which diallage and other gabbro con- 
stituents are occasionally present in the groundmass, and a second in 
which gabbro material forms a very large portion, either of the matrix 
or of the pebbly portion of the rock. In either case the rock is much 
altered, with the resulting formation of plagioclase and hornblende. 
The serpentine of the region was originally an olivine-enstatite rock 
and not a gabbro as has been supposed. 
The New Jersey Eleolite-Syenite.—The New Jersey Eleolite- 
syenite dyke described by Emerson’ is again studied by Kemp,’ who 
' 1Edited by Dr. W. S. Bayley, Colby University, Waterville, Me. 
?Mitth. d. geol. Landesanst v. Elsass-Loth., iv, 1892. 
5Amer. Jour. Science, iii, xxiii, p. 302. 
*Trans. N. Y. Acad. Sci., Vol. xi, p. 60. 
