THE BASIC MASSIVE ROCKS, ETC. 441 



norites of Scheerer are classed among the gabbros and the hypers- 

 thenites, and those of Esmark are said to belong partly with 

 these and partly with the diorites. 



In the year succeeding the appearance of Zirkel's book, as 

 has been stated, Rose x made the first microscopical examina- 

 tion of gabbros that has been recorded. He found among the 

 Silesian gabbros two varieties, one of which is black and con- 

 tains olivine, and the other green and free from olivine. Tscher- 

 mak 2 followed Rose with a description of some Austrian gab- 

 bros, and an announcement that many serpentines are altered 

 gabbros, and that Streng's forellenstein is only an olivine gabbro. 

 He concluded, further, that augite and diallage differ only in 

 physical properties, and therefore that gabbro "ist eine Abtheil- 

 ung des Diabas " (p. 168). 



In the few years succeding Tschermak's paper several con- 

 tributions of great importance were added to the literature of 

 the gabbros. Zirkel 3 recognized olivine varieties of these rocks 

 among the Tertiary formations on the islands off the west coast 

 of Scotland, and succeeded in showing that the hypersthenites 

 described by Macculloch from the island of Skye contain no 

 hyphersthene. He further pointed out as important the fact 

 that the plagioclase associated with diallage is rich in inclusions, 

 while that associated with ordinary augite is free from them. In 

 the same year Hagge 4 continued the work that had been so 

 ably begun by DesCloizeaux in 1864. He made a careful micro- 

 scopic examination of all the important gabbro and hyphersthe- 

 nite occurrences recorded, and reached a result very similar to 

 that of Des Cloizeaux. He found that very many of the rocks 



1 G. Rose : Ueber die Gabbroformation von Neurode in Schlesien, Erster, Theil. 

 Zeits. d. deutsch. geol. Gessel. XIX, 1867, p. 270. 



2 Die Porphyrgesteine Oesterreichs aus der mittleren geologischen Epoche. 

 Wien, 1869. 



3 F. Zirkel : Geologische Skizzen von den Westkuste Schottland. Zeits. d. 

 deutsch. geol. Gessell. XXIII, 1871, pp. 58 and 92. 



4 R. Hagge : Mikroskopische Untersuchungen uber Gabbro und verwandte 

 Gesteine. Kiel, 1871. 



