766 ALEXANDER N. WINCHELL 



which occurred at the contact of the sandstone and trap, was doubt- 

 less a modified quartzite. His "trachytic phonolite" is not fully 

 described, and correlation is uncertain. 



J. H. Kloos,' in 1871, described gabbro or hypersthenite, black 

 porphyry or melaphyre, porphyry and amygdaloid. The first named 

 was probably a gabbro and the second a diabase. 



Pumpelly,^ in 1873, described melaphyre, trap, and amygdaloid 

 without microscopic study; he distinguished three kinds of mela- 

 phyre, coarse-grained, fine-grained, and melaphyre porphyry. Cor- 

 relations of these names are impracticable, and would be misleading 

 rather than helpful. 



Marvine,3 in the same year, described melaphyre, trap, diorite, 

 and amygdaloid. Pumpelly later claimed, probably correctly, that 

 Marvine's diorite included samples of diabase, melaph3rre, and gabbro 

 but no true diorite. 



Streng,4 in 1877, described melaphyre, melaphyre porphyry, and 

 hornblende gabbro from the Kew^enawan of Minnesota. He pub- 

 lished chemical analyses of two of these which permit their corre- 

 lation on the quantitative basis (see Table III). 



Pumpelly, 5 in 1878, described the alterations which some of the 

 Keweenawan rocks had suffered in great detail, but brought to 

 light no additional varieties of the unaltered rocks. 



The same author,^ in 1880, identified eight or ten kinds of igneous 

 rocks in the Keweenawan (see the correlation table). He distin- 

 guished diallage from augite by means of the parting in the former, 

 and, in accordance with the usage at that time, called a massive 

 igneous rock containing plagioclase and diallage a gabbro, while one 

 containing plagioclase and augite he called a diabase. But in his 

 descriptions and illustrations, his diabase seems to have an ophitic 

 texture in all cases. His identifications of the various plagioclase 

 feldspars were all based on incorrect methods, so that his so-called 



1 J. H. KIoos, Zeitschrift der deutscheti geologischen Gesellschaft, p. 417, 187 1. 



2 R. Pumpelly, Geol. of Mich., Vol. I, Pt. 2, 1873. 



3 A. R. Marvine, ihid. 



4 A. Streng, N. J. Min. Geol., 1877. 



s R, Pumpelly, Proc. Amer. Acad., Vol. XIII, p. 285, 1878. 

 6 R. Pumpelly, Geol. Wis., Vol. Ill, pp. 27-49, 1880. 



