No. 379] REVIEWS OF RECENT LITERATURE, 535 
orthoclase, microcline, apatite, and sphene, with secondary chlorite, 
calcite, muscovite, epidote, and hematite. The microperthite and 
usually the biotite are in phenocrysts, the remainder of the minerals 
constituting a groundmass with the trachytic structure. The most 
basic of the dikes has the following composition : 
SiO, Al,O, FeO, FeO MnO, CaO MgO K,O NaO P20; Cl F Loss Tot. 
52:53 18.31 .34 6.43 15 345. 182 6.47 7.26 1-59 -40.32 1.16 = 99.93 
The magma from which the dike material was produced belongs to 
the foyaite type. The most acid of the dikes are syenite porphyries; 
the most basic are types of a rock that would seem to be too basic 
to be included in this group. 
recently been made by Smyth,' his subject being the dike of alnoite 
at Manheim, N. Y. The fresh rock, which is black, consists largely 
of biotite, and serpentine derived from olivine, and of some magne- 
tite, apatite, perofskite, and secondary calcite. Its weathered product 
is a soft golden-brown clay-like mixture of bleached mica, magnetite, 
perofskite, probably apatite, and some very fine-grained material of 
uncertain nature. 
Analyses of the fresh and the weathered rock calculated to 100 
per cent, and the proportion of loss for each constituent are : 
SiO, TiO, AlO, FeO, FeO MgO CaO K,O Na,O Ign Tot. 
Fresh 35-51 2.27 6.14 8.59 5.64 20.55 7-46 2.90 «71 
Weathered 33.40 2.93 7-95 16.86 1.49 13-54 5-30 +29 
Tar 27.31 00 370 48.97 45-10 92.27 74.97 -00 
About 27 per cent of the original rock has been removed by solution, 
causing its complete disintegration, and yet a great portion of its 
original components can be detected in its weathered product. 
Notes. — Hopkins? describes the brownstones of Pennsylvania 
from the economic standpoint. He gives a brief account of the 
microscopic structure of thin sections of the product of each of the 
working quarries in the state. 
Although the liebenerite-porphyry of Predazzo has long been 
regarded as a rock derived from some nepheline-bearing porphyry, 
no rock containing nepheline had been found in the Predazzo district 
1 Smyth, Jr, C. H. Bull. Geol. Soc. of Amer., vol. ix, p. 257- 
2 Appendix to Ann. Rep. Penn. State College, for 1896. 
