39.32 1.70 1448 2.01 8.73 .71 8380 11.11 .87 3.76 .61 5.25 2.57 
948 The American Naturalist. [November, 
The olivine and the orthorhombic pyroxene are serpentinized and the 4 
plagioclase altered as already indicated. i 
Camptonite Dykes in Maine.—In the gneiss of Androscoggin 
County, Maine, especially in the vicinity of Lewiston and Auburn, 
are a number of small dykes, some of which are of normal diabase, 
while others consist of camptonites. Olivine is abundant in several 
of the latter, and in such large grains as to be readily detected in the 
hand specimen. Olivine and augite are frequently in phenocrysts, 
while the last named mineral, hornblende and plagioclase make up 
the large part of the groundmass of the lamprophyres. An analysis a 
of material from one of the dykes yielded Merrill and Packard : : 
SiO, TiO, Al,0, FeO, FeO MnO CaO MgO K,O Na,O P,O,CO,H,0 
Predazzites and Pencatites.—Twenty specimens of predaz- 
zites and pencatites from various localities have been examined by A 
Lenecek' in order to determine whether the rocks contain brucite or 
not. The sections of the true predazzites were found to have a calcite 
groundmass, scattered through which are fibres of hydromagnesite, A 
supposed to be pseudomorphs after periclase, since cross sections of 
groups of fibres have a regular outline, and since one section of penca- 
tite from Canzacoli shows periclase crystals more or less changed to 
serpentine. The dark pencatites differ from the predazzites in contain- 
ing a large quantity of marcasite, to whose opacity the dark color of 
the rock is due. Besides the constituents already mentioned there are 
in both rocks many small grains of colorless silicates that may be 
pyroxenes, amphibole and olivine. Serpentine veins also cut both 
rocks, and brucite plates are not uncommon as the lining of little 
cracks. 
Petrographical News.—Around the granite boss of Cima 
d’Asta, as around the other eruptive masses of eastern South Tyrol, 
there are abundant evidences of contact action in the contiguous sedi- 
mentaries, the contact rocks being not different in their essential 
characteristics from those surrounding the Adamello tonalite. The 
tonalite gneiss of the Adamello region is a pressure gneiss, occurring 
along lines, which were the slipping directions in the eruptive. 
ĉAm. Geol., x, 1892, p. 
Min, u. Petrog. Mitth., xii, La 429. 
8Sdlomon. Min. u. Pero, Mitth. xii, p. 408. 
