382 /. MORGAN CLEMENTS 



their importance. The following analysis gives its chemical 

 composition : 



ANALYSIS OF BRONZITE-NORITE BY MR. GEORGE STEIGER. 



Si0 2 



Ti0 2 



A1 2 3 



Fe 2 ; 



FeO 



CaO - 



MgO 



KoO- 



The last gabbro occurrence to be mentioned is one in which 

 we find the normal type of hornblende-gabbro cut by a dike in 

 which monoclinic pyroxene is in about equal quantity with the 

 hornblende. This evidently represents a transition towards a 

 true gabbro. This exposure of gabbro is cut by a peridotite, 

 which is feldspathic and concerning which detailed statement 

 will be made in the following pages. 



The rocks just described may be compared in their varia- 

 tion to those described by G. H. Williams * from Maryland, by 

 Chester 2 from Delaware, and by Fairbanks 3 from California. A 

 series of basic rocks similar in many respects to those of Crys- 

 tal Falls has also been described recently in two interesting 

 papers by van Horn 4 and Schaefer. 5 



Peridotites. — The peridotites are all coarse-grained rocks of 

 very dark color, consisting of the following chief mineral con- 



T The gabbros and associated hornblende rocks occurring near Baltimore, by 

 G. H. Williams, Bull. U. S. Geol. Surv., No. 28, 1886. Outline of the geology of 

 Maryland, Baltimore, 1893, p. 39. 



2 The gabbros and associated rocks in Delaware, by F. D. Chester, Bull. U. S. 

 Geol. Surv., No. 59, 1890. 



3 The geology of Point Sal, by H. W. Fairbanks, Bull. Dept. of Geol., Univ. of 

 Cal., Vol. II, No. I, 1896, p. 56 et seq. 



4 Petrographische Untersuchungen liber die noritischen Gesteine der Umgegend 

 von Ivrea in Oberitalien, by F. R. van Horn, Tsch. Mitt , Vol. 17, 1897, pp. 391- 

 420. 



5 Der basische Gesteinszug von Ivrea im Gebiet des Mastallone-Thales, by R. W. 

 Schaefer, Tsch. Mitt., Vol. 17, 1898, pp. 495-517. 



