FETTKE, MANHATTAN SCHIST OF NEW YORK 225 



If any evidence of contact metaniorphism could be found, this would 

 still further corroborate the igneous origin of the hornblende schist. As 

 already mentioned, the only occurrence obsen^ed by the writer which 

 might indicate such a contact zone was the occasional presence near such 

 a contact of isolated hornblende crystals in the mica schist which were 

 similar in appearance and optical properties to those of the hornblende 

 schist. 



The relation of the hornblende schist to the mica schist is such as might 

 readily result from the intrusion of a series of sheets parallel to the bed- 

 ding of the schist. Such a relation would also result if the igneous rock 

 had been poured out as a lava flow at successive intervals during the 

 period of deposition of the sediments from which the mica schist was de- 

 rived. This would, however, necessitate the occurrence of numerous 

 periods of igneous activity followed by periods of deposition of fine argil- 

 laceous sediments, as the sheets probably occur at various horizons in the 

 schist over practically the whole area under consideration. The same 

 would be true if they represented metamorphosed interbedded basic tuffs. 

 It is much more reasonable to suppose that the igneous rock was intruded 

 at numerous horizons in the sediments after their deposition in the form 

 of intrusive sheets or sills. The fact that the hornblende schist does oc- 

 casionally cut across the foliation or bedding further corroborates such a 

 view. The only peculiar feature about the hornblende schist, if the above 

 interpretation is correct, is that it has never yet, to the writer's knowl- 

 edge, been found cutting the Inwood limestone. The probable explana- 

 tion for this is that the limestone did not part readily along its bedding' 

 planes and the intrusive simply passed up through it along fissures which 

 are not at present exposed. 



From the foliated structure of the hornblende schist and its relation to 

 the mica schist, it is quite evident that it was intruded into the original 

 sediments prior to the period of folding and regional metamorphism. 

 Both have been folded and crumpled with equal intensity and have been 

 completely recrystallized. They now possess a marked foliated structure 

 and a medium to coarsely crystalline texture. J. J. H. TealP^ has de- 

 scribed a similar hornblende schist from Scourie, on the northwest coast 

 of Scotland, which can be traced through various stages of metamorphisni 

 into an original diabase dike. Analyses of this hornblende schist and 

 diabase are quoted in a previous paragraph. The hornblende schist is 

 made up of deep green hornblende, quartz, feldspar, ilmenite, sphene and 

 apatite. The diabase consists of feldspar, augite, ilmenite, apatite and 

 minor secondary products including hornblende, chlorite, quartz and 



"Quart. Jour. Geol. Soc, Vol. 41, pp. 133-145. 1885. 



