Page:The Journal of geology (IA journalofgeology11893univers).pdf/18

masses, in their upper portions the diallage is replaced in large part by augite. Many other papers of importance were published, and in most of these the structure of the rocks described was more or less briefly alluded to. Wiik^[1] announced the fact that many of the Finnish rocks classed by Zirkel among the hypersthenites are olivine-diabases and olivine gabbros, while Stelzner^[2] filled the gap thus produced in this group by the discovery of a bronzite gabbro from the Monte Rosa district in the north of Italy. Vallee-Poussin and Renard^[3] made a thorough examination of the plutonic rocks of Belgium and the eastern part of France, and discussed the composition and structure of some gabbros.

The result of these and other workers were collected and edited by Rosenbusch^[4] in his well-known book on the microscopical characters of massive rocks, in which the fixing of rock types which had been begun by Zirkel was carried out in a scheme which was not improved upon until the same author published the second edition of his treatise ten years later^[5]. In the scheme proposed in 1877, the gabbros were placed among the pre-Tertiary massive granular rocks. The group was made to include all pre-Tertiary rocks consisting essentially of diallage and plagioclase in their unaltered state, either with or without olivine. Saussurite was recognized as a secondary product produced by the alteration of plagioclase, and green hornblende (actinolite and smaragdite) as the result of an alteration of diallage. The saussurite and the hornblende gabbros were no longer