1892.] Mineralogy and Petrography. 767 
and monchiquite. The bostonite® is usually of a creamy or brownish 
white color. Its structure is typically trachytic, with a few phenocrysts 
of orthoclase in a groundmass composed of rods of this mineral and 
of anorthoclase, and between these little masses of quartz. No dark 
silicates occur in any of the sections examined. An analysis of the 
rock gave: 
SiO, ALO, FeO, CaO MgO K,O NaO Loss Total. 
62.28 1917 339 144 tr 593. 5.37 2.33=99.91 
The specific gravity is 2.648. In several places dykes were noted in 
which the bostonite cements angular pieces of other rocks forming an 
eruptive breccia. The included fragments are sometimes slate and red 
quartz that show no effects of contact action, and sometimes rounded 
masses of norite, quartzite and limestone, whose shapes are due largely 
to absorption by the eruptive. The monchiquites consist chiefly of 
zonal augite, brown hornblende and biotite crystals, and olivine in a 
feebly refractive groundmass that may be an altered glass. The augite 
and hornblende are in two generations and the other minerals in but 
one. An analysis of one specimen gave: 
SiO, AlO, Fe,O, FeO CaO MgO K,O Na,O Loss Total 
40.87 17.86 1445 .38 17.61 163 83 1.29 447=98.89° 
Besides the two types mentioned there occur also in the region many 
dykes of diabase and camptonite. 
The Serpentine of the East Central Alps.—The serpentine 
occurrences within a restricted area in the East Central Alps have 
been examined by Weinshenck’ with a view to learning something of 
the origin of the rock. Its irregular masses imbedded in crystalline 
schists consist of serpentine, tale, ete., that were formed by the alter- 
ation of a pyroxenic aggregate. At the contact of the rock with the 
neighboring schists has been produced a great variety of hornstones, 
among which may be mentioned garnetiferous and epidotic kinds 
containing much diopside, vesuvianite, ete. The existence of contact 
effects around the serpentine and the presence of dykes of the latter 
rock in the surrounding schists indicate to the author that the mother- 
rock of the serpentine was an eruptive pyroxenite. 
5AMERICAN NATURALIST, 1891, p. 573. 
6Given as 99.39 in original. 
7Habilitationsschrift. München, 1891. 
