THE BASIC MASSIVE ROCKS, ETC. 447 



and of types intermediate between these, was established at the 

 time that Rosenbusch's book appeared. In this year (1877) 

 Tornebohm 1 suggested that the name hyperite be used for the 

 latter classs, composed essentially of plagiocla'se, diallage and 

 an orthorhombic pyroxene, that the term gabbro should be used 

 to designate plutonic rocks in which the pyroxene is diallage, and 

 that hyphersthenite (or norite) should be restricted to those 

 containing a rhombic pyroxene as their principal augitic constit- 

 uent. This suggestion has not met with a very wide acceptance 

 because the gradation between the three types is very gradual, 

 and in all cases the geological relations of the types are the 

 same. It is convenient, however, as a descriptive name for those 

 gabbros containing two pyroxenes. 



In the same year Streng 2 investigated the crystalline 

 rocks of Minnesota and described a gabbro from near Duluth, 

 in that State, to which he gave the name hornblende -gabbro, 

 because of the supposition that the brown hornblende it 

 contains is primary. Irving, 3 however, has shown that 

 much of the brown hornblende in the rocks of the Lake 

 Superior region is secondary. He thought that nearly all, if not 

 all, of the hornblende of the hornblende gabbros is of this 

 nature. Williams 4 has also shown that compact brown horn- 

 blende is often a secondary product of the alteration of augite ; 

 and Wadsworth 5 holds to the view that this is the character of 

 all the hornblende in the Lake Superior gabbros. 



J A. E. Tornebohm: Ueber die wichtigsten Diabas und Gabbrogesteine 

 Schweden. Neues Jahrb. f. Min., etc., 1877, p. 387. 



2 A. Streng and J. H. Kloos : Ueber die krystallinischen Gesteine von Minne- 

 sota in Nord Amerika. Neues Jahrb. f. Min., etc., 1877. 



3 R. D. Irving : On the Paramorphic Origin of the Hornblende of the Crystal- 

 line Rocks of the Northwestern States. Am. Jour. Sci., Vol. XXVI, 1883, p. 27 ; lb. 

 XXVII, 1884, p. 130. 



4 G. H. Williams : On the Paramorphosis of pyroxene to hornblende in Rocks. 

 Am. Jour. Sci., XXVIII, 1884, p. 259. 



s M. E. Wadsworth : Preliminary Description of the Peridotytes, Gabbros, 

 Diabases and Andesytes of Minnesota. Bull. No. 2. Geol. and Nat. Hist. Surv. of 

 Minn., St. Paul, 1887, p. 66. 



