768 ALEXANDER N. WINCHELL 



between augite and diallage as a basis of rock classification, and yet, 

 like Irving, he used it. He did not discriminate sharply between 

 the ophitic and the poikilitic textures, both of which may be found, 

 sometimes together, in Minnesota diabases. 



Bayley,^ in 1889-97, described the gabbro bathylith of Minne- 

 sota in considerable detail, and also studied the peripheral phases 

 of the gabbro. To emphasize the close connection in origin between 

 the peridotite and the gabbro of the district, he called the former 

 nonfeldspathic gabbro. Although some of the peripheral phases 

 described by Bayley may be of later date than the gabbro, if we 

 assume that they all belong in the Keweenawan, we find that Bayley 

 recognizes not only augite syenite of Irving, but also a porphyritic 

 equivalent which he calls quartz keratophyre on account of the 

 presence of anorthoclase. He speaks of olivine pyroxene aggregates 

 which should apparently be correlated with wehrlite, dunite, and 

 pyroxenite. 



In the peripheral phases he finds a texture which he considers 

 somewhat characteristic; it consists of the presence of many rounded 

 grains of the more important constituents inclosed by other minerals. 

 Bayley calls it the granuHtic texture. It has been called the contact 

 structure by Salomon, and the globular by Fouque. It is well 

 described by the term globular or globulitic. 



Grant, ^ in 1893 and 1894, described gabbro, diabase, granite, and 

 fine-grained rocks previously called muscovadites in the Minnesota 

 reports. Grant's granite is the equivalent of Irving's augite syenite, 

 later called soda augite granite by Bayley (see the correlation table). 

 The fine-grained rocks, called muscovadites, include border facies of 

 the gabbro mass of various types, but especially norite, fine grained 

 gabbro often with hypersthene, olivine norite, cordierite norite, etc. 



Hubbard, 3 in 1898, described various types of the Keweenawan 

 of Keweenaw Point. His melaphyre is chiefly andesite or basalt; 



1 W. S. Bayley, Am. J. Sc, Vol. XXXVII, p. 54, 1889; Vol. XXXIX, p. 273, 

 1890; U. S. G. S., Bull. 109, 1893; J. G., Vol. I, p. 433, 1893; Vol. II, p. 814, 1894;- 

 Vol. Ill, p. I, 1895; U. S. G. S., Mon. 28, p. 519, 1897. 



2 U. S. Grant, G. N. H. S. Minn., 21st Ann. Rep., p. 5, 1893; 22d Ann Rep., 

 p. 76, 1894. 



3 L. L. Hubbard, Geol. Surv. Mich., Vol. VI, Pt. 2, 1898. 



