No. 387.] REVIEWS OF RECENT LITERATURE. 279 
and for the investigation of scientific methods of highway con- 
struction, following the lead, in this last respect, of the State of 
Massachusetts. T. A. Jacare JR. 
PETROGRAPHY. 
Granites and Diabases. — Milch’s’ article on the granitic rocks 
of the Riesengebirge and Bodmer-Beder’s? paper on the olivin dia- 
base from the Plessurgebirge in the Grisons are monographic presen- 
tations of the subjects they discuss. In the first, the author describes 
in great detail, and with a wealth of chemical analyses, the well-known 
granitite of the Riesengebirge, together with its basic and acid phases 
and the concretions they contain. Chemically, the rock is a mixture 
of Rosenbusch’s granitic and dioritic magmas. The acid and basic 
phases are regarded as differentiation products of the magma that 
yielded the normal rock. Even the dike granites and the pegmatites 
of the district are looked upon as ‘‘ Schlieren ” in the granitic magma, 
formed by the solidification of the mother liquor left after the greater 
portion of the magma had crystallized. The basic phases of the 
rock often present the features of kersantites. They appear as con- 
cretions in the granitite and as dark “ Schlieren” traversing it. 
The diabases of the Plessurgebirge in the neighborhood of Chur 
occur as stocks, as horizontal sheets, and as dikes in the predomi- 
nant limestone. In the center of the stocks its structure is gran- 
ular; nearer the peripheries of the masses it is ophitic, and on the 
peripheries it is vitrophyric. Varioles and vacuoles are present as 
contact phenomena. The former are spherulites of radial plagioclase, 
and the latter amygdaloidal cavities that have been filled with albite, 
quartz, and calcite. The rocks present no unusual features, but the 
paper is worth examination because of its thoroughness in describing 
and picturing each structural form of the rock investigated and of 
its constituents. 
Granitic Oceanic Islands and the Nature of Laterite.— The 
small group of tropical oceanic islands, known as the Seychelles, are 
noteworthy from the fact that they are neither of coral nor of vol- 
canic origin, but are granitic in character. Bauer? reports that they 
consist principally of granites, and syenites cut by dikes and covered 
1 Neues Jahrb. f. Min., Bd. xii, p. 115. 2 Ibid., p. 238. 
8 Neues Jahrb. f. Min., etc. Bd. ii (1898), p. 163. 
