GABBEO AND NORITE INTRUSIVES. 247 



xenomorphic individuals, forming a somewhat smaller proportion of the 

 gi'oundmass than does the liornblende, but is more abundant than the 

 bronzite of the groundmass. Sphene is present in considerable quantity, 

 and likewise ilmenite (fig. A, PI. XLV). 



This rock stands between the hornblende-gabbros and the norites. In 

 texture it might be compared with the norite-porphyrite (enstatite-porphyrite 

 of Rosenbusch) with holocrystalline groundmass. But it differs essentially 

 from this rock in the presence of a large quantitj^ of hornblende. This 

 hornblende connects it with the hornblende-gabbros, from which its content 

 of pyroxene, both orthorhombic and monoclinic, tends to separate it. Owing 

 to its obvious relation to the bronzite-norites, which, like it, occur as differ- 

 entiation facies of and dikes in the hornblende-gabbro, I shall call it a 

 "bronzite-norite-porphyry," using the term "porphyry" purely in a textural 

 sense. 



The rocks may be compared, in their variation, to those described by 

 G. H. Williams from Maryland,' by Chester from Delaware," and by Fair- 

 banks from California.' A series of basic rocks similar in many respects 

 to those of Crystal Falls has also recently been described in two interest- 

 ing papers by Van Horn * and Schaefer.^ 



DYNAMICALLY ALTERED GABBRO. 



Near tlie junction of sees. 26, 27, 33, Si, T. 43 N., R. 31 W., there is 

 a large gabbro mass which shows marked evidence of dynamic action, and 

 may well be cited as an example of a metamorphosed gabbro, or, perhaps 

 more clearly, as a rock intermediate between a hornblende-gabbro and a 

 hornblende-gneiss. None of the gabbros thus far described show any evi- 

 dence of having taken part in very extensive progenic movements. The 

 minerals of but few of them show more than the common phenomenon of 

 slight wavy extinction. Hence it is clear that their intrusion took place 



'The gabbros and associated hornblende rocks occurring near Baltimore, by G. H. Williams: 

 Bull. U. S. Geol. Survey No. 28, 1886 ; Outline of geology of Maryland, Baltimore, 1893, p. 39. 



^The gabbros and associated lOcks in Delaware, by F. I). Chester: Bull. U. S. Geol. Survey 

 No. 59, 1890. 



^The geology of Point Sal, by H. W. Fairbanks: Bull. Dep. Univ., California, Vol. XI, 1896, 

 p. 56 et seq. 



^Petrographische Uutersuchungen iiber die noritischen Gesteine der Umgegend von Ivrea im 

 Oberitalieu, by F. R. van Horn : Tscliermaks mineral., Jlittheil., Vol. XVII, 1897, Part V, pp. 391-420. 



'■ Der basische Gesteinzug von Ivrea im Gebiet des Mastallone-Thals, by R. W. Schaefer: Tscher- 

 maks mineral., Mittheil., Vol. XVII, 1898, Part VI, pp. 495-517. 



