FETTKE, MANHATTAN SCHIST OF NEW YORK 239 



the schist usually have also a xevy high content of feldspar, a portion of 

 which was undoubtedly derived from the pegmatite. Cyanite occasionally 

 appears, in long bladed crystals having a slight bluish tinge, in portions 

 of the schist which have been thoroughly saturated with pegmatitic ma- 

 terial. In this case, it is apparently of contact metamorphic origin. 

 Undoubtedly the pegmatites derived a portion of their constituents from 

 the rocks through which they were intruded. Such minerals as garnet 

 and biotite probably owe their origin to this source. Black tourmaline 

 similar in every respect to that found in the pegmatite itself often occurs 

 in the mica schist in the vicinity of the pegmatitic intrusions and has 

 evdently resulted from the emanations from this source. 



That these granitic and pegmatitic intrusions played a very important 

 role in the metamorphism and recrystallization of the original shale of the 

 Manhattan formation into mica schist, there can be but little doubt. 

 Most of the water associated with the intrusions must have been given off 

 when solidification occurred, since it does not enter into the composition 

 of any of the resulting minerals to any extent. This water must have 

 been very effective in bringing about recrystallization. The local tem- 

 perature must also have been raised by these intrusions. Edson S. Bas- 

 tin*^ in his study of the Maine pegmatites has come to the conclusion that 

 they crystallize at a temperature in the neighborhood of 575° C. The 

 New York pegmatites are very similar to the Maine occurrences. These 

 intrusions must, therefore, be regarded as very effective agents in the 

 metamorphism of the original shale into mica schist. Other influences 

 were the deep burial beneath overlying sediments and the severe folding 

 and crumpling which followed the deposition of the original sediments. 



Bedford "Augen" Gneiss 



In discussing the mica schist in the vicinity of Bedford Village, men- 

 tion has already been made of the "augen" gneiss which is so frequently 

 associated with it. The region in which the structure occurs covers an 

 ovoid area southeast of Bedford Village. The long axis extends in a 

 northeast-southwest direction and has a length of about six miles. The 

 width does not exceed two and one-half miles. 



The "augen" structure is developed in two types of rock, a mica schist 

 and a hornblende schist, but the entire area does not have the "augen" 

 structure. It appears in bands usually parallel to the foliation. The 

 bands grade into the ordinary schist by the gradual disappearance of the 

 "augen" (PI. X, Fig. 2). Sometimes the "augen" stop rather suddenly. 



«U. S. Geol. Surv. Bull. No. 445. p. 45. 1011, 



