180 abstracts: petrology 



and of following carefully the course of dehydration under prescribed 

 conditions. Detailed directions are given for such tests and for avoid- 

 ing several sources of error. 



Attention is also called to two fairly constant associates of metahewet- 

 tite. One of these (also a constituent of carnotite ores) is a gray hydrous 

 silicate of aluminum, trivalent vanadium, and potassium. The other 

 is elemental selenium, the existence of which as a mineral species seems 

 now for the first time estabhshed. W. F. H. 



PETROLOGY. — An occurrence of pyroxenite and hornhleyidite in Bahia, 

 Brazil. Henry S. Washington. Am. Jour. Sci. (4), 38: 79-90. 

 1914. 

 The igneous mass occurs near Maracas, in the State of Bahia, intruded 

 into gneisses. The central part is a hornblendite and the outer a pyrox- 

 enite, both being exceptionally fresh. Complete analyses of the two are 

 given and their relations to other occurrences are discussed. Both 

 rocks are notable for the large amount of manganese which they con- 

 tain, which is correlated with the abundance of manganese ores in this 

 part of the State of Bahia. There is also a notable amount of copper. 



H. S. W. 



PETROLOGY. — The mode of formation of certain gneisses in the High- 

 lands of New Jersey. Clarence N. Fenner. J. Geology, 22: 

 594-612; 694-702. 1914, 

 The paper deals with certain geological phenomena which have been 

 observed in an area of ancient crystalline rocks in northern New Jersey, 

 and discusses the manner in which the structures in question have 

 originated. The manner of action of the processes is considered, not 

 only from the geological side, but also from physical and chemical stand- 

 points. A description is first given of the structural relations of the 

 gneisses as observed in the field, and evidence is presented leading to 

 the behef that at this locaHty the foliation of the gneisses can not well 

 be attributed to the squeezing-out of a partly differentiated magma or 

 to the shearing and recrystalHzation of a solidified rock, ]:)ut that its 

 origin must be looked for in a process involving the injection of a thinly 

 fluid granitic magma between the layers of an original rock of a lamin- 

 ated character. Evidence is found which indicates that the process of 

 injection was carried out in a most quiet and gradual manner, and pos- 

 sessed many of the characteristics of a substitution of the original ma- 

 terial by the magmatic solution rather than the features of a violent 

 intrusion. The observed relations are very similar to those which cer- 

 tain French geologists have described under the name of lit-par-lit in- 



