738 The American Naturalist. [August, 
SiO, TiO, Al,O, Fe,O, FeO MnO MgO CaO Na,O K,O H,O P,O, CI Total 
46.73 78° 10.05 3.53 8.20 28 9.68 13.22 181 3.76 1.24 151 18=100.97 
The rock is. thus a granular plutonic rock consisting essentially of 
augite and orthoclase. It is closely related to augite-syenite, bearing 
the same relation to it as vogesite does to hornblende-syenite. 
The white rock associated with the shonkinite is a sodalite-syenite, 
containing as its bisilicate component only amphibole. Its composition 
is given as follows: 
SiO, TiO, Al,O, Fe,O, FeO MnO MgO CaO Na,O K,O H,O P,O, Cl Total 
56.45 29 20.08 1:31 439 .09 63 214 5.61 718 1.77 13 .43—=100.45 
The basic rock is richer in iron, magnesia and lime than the acid one; 
since the two rocks pass into each other by a rapid but continuous 
gradation, they are believed to be of the same age and to be the com- 
plementary differentiated portions of the same magma. The differen- 
tiation in this case could not have been due to a process of crystalliza- 
tion, in which the first crystallized minerals were accumulated in the 
peripheral portions of the cooling magma, since the other iron-bearing 
components of the shonkinite and of the syenite are so radically different. 
The differentiation must have occurred in the magma while still molten. 
The Serpentines of the Central Alps.—Three years ago Wein- 
schenck* gave a preliminary account of the serpentines of the East 
Central Alps and their contact effects, showing that the former were 
originally pyroxene eruptives. In a recent paper he returns to the 
subject,‘ and in a well illustrated article gives in detail the reasons for 
his former conclusions. He finds upon the examination of a large 
suite of specimens that the original rock was an olivine-antigorite aggre- 
gate, which he names stubachite, from its most important locality. 
The antigorite is believed to be an original component and not an alter- 
ation product of the olivine, as it is found intergrown with perfectly - 
fresh grains of the latter mineral. The grate structure (“ Gitter- 
structur”) of many serpentines is ascribed to such intergrowths, and 
not to the alteration of pyroxene along its cleavage planes. ‘The orig- 
inal stubachite was a medium grained holoerystalline, allotriomorphic 
rock of intrusive igneous origin, which has not suffered much altera- 
tion since its exposure by erosion. 
* American Naturalist, 1892, p. 767. 
t Abhand. d. k. bayer. Ak. d. Wis II, Cl. XVIII, Bd. p. 653. 
