THE BASIC MASSIVE ROCKS, ETC. 439 



are nothing but altered forms of the fresh gabbro. It is rather 

 surprising to one accustomed to the use of the microscope as a 

 means of studying rocks to learn that such correct conclusions 

 as to the inner constitution of rock masses co-uld be reached 

 without the aid of this instrument as were reached by Streng in 

 his study of these rocks. 1 A few years later the same geologist 

 examined the gabbros and serpentines of Neurode in Silesia and 

 discovered that all of the so-called hypersthene of these rocks 

 is probably diallage, and that the serpentine rock, which from 

 very early times had been known under the name of forellen- 

 stein, is really an altered gabbro, containing but a small amount 

 of pyroxene. While Streng was examining the rocks of Silesia 

 and deciding that the so-called hypersthenite is a true gabbro, 

 Des Cloizeaux, 2 was investigating the hypersthenites and gabbros 

 of France, with a view to their better classification. Des 

 Cloizeaux declared as the result of his investigations that dial- 

 lage, which is only a lamellar augite, and saussurite form eupho- 

 tides and gabbros, and that many rocks that had been called 

 hypersthenites or hyperites contain no hypersthene, but that the 

 supposed hypersthene is diallage. He further proposes that dis- 

 tinctions between gabbros and hypersthenites be made more clear 

 by the use of the name diallagite for labradorite and diallage 

 rocks, and hyperite for those composed of labrodorite and 

 hypersthene or bronzite. Although the use of Des Cloizeaux's 

 name diallagite was not accepted by petrographers, all workers 

 acknowledged the correctness of the statement that very many 

 of the hypersthenites described from various localities are noth- 

 ing more than gabbro in which the cleavage of the diallage is 

 well marked. 



Thus far the study of the gabbros and related rocks had pro- 

 ceeded without the aid to be obtained from the microscope. 

 Many rocks had been described as belonging to the gabbro -type, 



1 A. Streng : Ueber den Serpentinfels und Gabbro von Neurode in Schlesien. 

 Neues Jahrb. f. Min., etc., 1864, p. 257. 



2 Alf. Des Cloizeax : Sur les Classifications des roches dites hyperites et eupho- 

 tides. Bull. Soc. Geol. d. Fr. XXI, 1864, p. 105. 



