458 A. A. JULIEN AMPHIBOLE SCHISTS OF MANHATTAN ISLAND 



We may next compare the analysis of our schist (IV) with those pub- 

 lished of similar schists from American and foreign localities : 



XXIII. Gabbro diorite, derived from hypersthene gabbro. Windsor road, Balti- 

 more, Maryland. G. H. Williams. 



This consisted of hornblende andanorthite, with pyrite, garnet, epidote, zoisite, 

 apatite, magnetite, and, rarely, rutile and titanite. 



XXIV. Hornblende schist, from gabbro. Lower Qainnesec basin, Wisconsin. 

 R. B. Riggs. 



XXV. Hornblende schist, from diabase. Lower Quinnesec falls, Wisconsin. 

 R. B. Riggs. 



This consisted of brown hornblende, chlorite, epidote, quartz, and feldspar, with 

 menaccanite, leucoxene, rutile, pyrite, and calcite. 



XXVI. Amphibole schist, from diabase porphyrite. Near Brown's valley, Cal- 

 ifornia. W. P. Hillebrand. 



XXVII. Hornblende schist, from diabase. Grand Rapids, Wisconsin. M. 

 Swenson. 



It contained also FeS, 0.73 ; CaPjOs, 1. 10, and traces of 01 and Fl. Percentage con- 

 stitution : Hornblende, 65.2; orthoclase, 19.2; oligoclase, 9.1 ; apatite, 0.4; bio- 

 tite, 2.0; magnetite, 0.4 ; pyrite, 0.7; limonite, hematite, and water, 1.3; quartz, 

 1.7, and generally some augite. 



XXVIII. Hornblende schist, from diabase. Near Cleveland mine, Michigan. 

 R. B. Riggs. 



This consisted of hornblende and labradorite, with pyrite. 



XXIX. Hornblende schist, from diabase. Marienhohe, Germany. H. Rosen- 

 busch. 



XXX. Zoisite amphibolite, from diabase. Loisberg, Germany. H. Rosenbusch. 



XXXI. Actinolite rock, from diabase. Schapbachthal, Germany. H. Rosen- 

 busch. 



Concerning the derivation of the last three rocks Rosenbusch states : "They 

 bear fully the character of eruptive rocks. They agree very satisfactorily with the 

 composition of many diabases and gabbros (in part, rich in olivine)."* 



XXXII. Schalstein, from diabase. Reitsch, Germany. R. Weinholdt.f 



This is added to represent an intermediate stage of alteration between 

 a diabase and hornblende schist, and selected on account of its low per- 

 centage of silica, like that of our hornblende schist (IV). 



*^Loc. cit., p. 58. 



t Tsch.' min. u. pet. Mitth., 1871, p. 108. 



