444 THE JOURNAL OF GEOLOGY. 



masses, in their upper portions the diallage is replaced in large 

 part by augite. Many other papers of importance were publish- 

 ed, 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 dis- 

 covery 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 micro- 

 scopical 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 pro- 

 duced by the alteration of plagioclase, and green hornblende 

 (actinolite and smaragdite) as the result of an alteration of dial- 

 lage. The saussurite and the hornblende gabbros were no longer 



1 F. J. Wiik : Mineralogiska och petaografiska meddelanden. Ref. Neues Jahrb. 

 f. Min., etc., 1876, p. 206. 



2 A. Stelzner: Briefliche Mittheilung. Zeitz. d. d. geo . Gessell., XXVIII. 

 1876, p. 623. 



3 Ch. de la Vallee-Poussin, et A. Renard : Memoire sur les caracteres miner- 

 alogiques et stratigraphiques des roches dites plutoniennes de la Belgique et de 1' 

 Ardenne francaise. Bruxelles, 1876, pp. 62-76 and 125-128. 



4 H. Rosenbusch : Mikroskopische Beschaffenheit der Massigen Gesteine. 

 Stuttgart, 1877. 



SH. Rosenbusch: Mikroskopische Beschaffenheit der Massigen Gesteine. 2te 

 Aufl. Stuttgart, 1887. 



