THE BASIC MASSIVE ROCKS, ETC. 435 



province, which the writer desires to make as opportunities and 

 time permit. The present plan proposes a series of papers ap- 

 pearing in this Journal at irregular intervals. The first follows 

 this introduction. The second will embrace a sketch of previous 

 work on the basic rocks of the region, and the succeeding ones 

 will treat of the gabbros and coarse diabases in the Huronian 

 and Keweenawan areas on both sides of the lake. 



I. BRIEF HISTORY OF THE CLASSIFICATION OF THE GABBROS 

 AND NEARLY RELATED ROCKS. 



At about the same time the names Euphotide and Gabbro 

 were applied, respectively by Haiiy 1 in France and von Buch 2 in 

 Germany, to rocks composed essentially of a foliated augite and 

 a "compact feldspar." Haiiy describes the Euphotides as con- 

 sisting of a compact feldspar and diallage, for which combina- 

 tion he constructed the name from the two Greek words ev 

 (blessed) and <£ws (light), in allusion to the green and white 

 mottling in the hand-specimens from many localities. Von 

 Buch's name, gabbro, was adopted from the Florentines 3 to 

 cover a group of rocks that had been described at various times 

 under a great number of different names, of which perhaps jade 

 was the most common. Although gabbro was used by the 

 Italians to designate what is now known as a diallagic serpen- 

 tine, it has been accepted by nearly all geologists outside of 

 France as the name to be applied to the group of rocks which 

 von Buch so clearly and definitely separated from other allied 

 rocks, and defined as made up of jade, feldspar and smaragdite. 



Between the time of the appearance of von Buch's paper and 

 the publication of the first microscopic description of gabbros 

 by Rose in 1867, 4 many descriptions of these rocks appeared in 



'Traite de Mineralogie, 2d Ed., IV., p. 535. 



2 Ueber den Gabbro, mit einigen Bemerkungen iiber den Begriff einer Gebirgsart. 

 Geol. natur. f. Freund. zu Berlin, Mag. etc., 1810, IV., p. 128; 1816, VII., p. 234. 



3Cf. T. S. Hunt: Contributions to the History of Euphotide and Saussurite. 

 Am. Jour. Sci., 2d Series, Vol. XXVIL, 1859, p. 336. 



4 G. Rose. — Ueber die Gabbroformation von Neurode in Schlesien. Erster Theil. 

 Zeits. d. deuts. Geol. Ges. XIX., 1867, p. 270. 



