178 THE AMERICAN NATURALIST.  [Vou. XXXIII. 
An Acid Pegmatite in a Basic Rock. — An interesting occurrence 
of an acid pegmatite in a basic rock is described by Jaggar.’ It 
exists as lenticular or vein-like masses that merge gradually into the 
diabase forming the Medford dike in the Boston basin. As the 
pegmatite, which is a quartz-microcline aggregate, is approached, 
the white plagioclases of the diabase acquire a salmon-colored zone 
of more acid material. The plagioclase finally disappears and micro- 
cline takes its place. At the same time quartz replaces all the bisili- 
cates. In some places the pegmatite appears to have been infiltrated 
into miarolitic spaces. Quartz inclusions in the diabase are often 
surrounded by inner zones of micropegmatite and outer ones of 
augite. The latter are the usual reaction rims so frequently dis- 
covered around acid inclusions in basic magmas. Within these the 
liquids bearing the pegmatite-producing minerals deposited their 
burdens and at the same time corroded the quartz of the nucleus. 
The conclusion arrived at, to the effect that granophyric intergrowths 
of quartz and feldspar are not necessarily primary growths, seems to 
be well substantiated. 
Notes. — Vogt? gives a résumé of the facts bearing on the theory 
of deposition of ore bodies by differentiation processes in eruptive 
magmas. He points out that in the same magma we often find 
oxidation products, sulphides and metals, all of which must be 
regarded as normal differentiation products of the rocks in which 
they occur. The facts of differentiation are well known, but of the 
cause of differentiation we are yet ignorant. 
Three kersantite® dikes cut the kamm-granite north of the Leber- 
thal near Markich in Elsass, and several sheets and dikes of quartz 
porphyry occur in the Robinatthal. 
The crystalline rocks of southeastern New York, east of the 
Hudson, are granites, gneisses, mica-schists, serpentine and basic 
and acid intrusives. Merrill* reports the oldest of these rocks to be 
a hornblende granite. This forms the central mass of the Highlands. 
On its flanks are banded gneiss composed of orthoclase and quartz, 
biotite and hornblende and containing beds of magnetite; and 
associated with this is the well-known mica-schist of the district. 
1 Amer. Geol., vol. xxi (1898), p. 203. 
2 Compte-rendu du cong. géol. intern. 6e Sér. (1894), p. 382. 
3 Bruhus, W. Mitth. d. geol. Landesanst. v. Elsass-Loth., vol. iv (1897), 
p. Cxxix. 
4 Merrill, F. J. H. New York State Museum Report (1896), p. 21. 
