BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 4, pp. 167-178, pl. 3 February 27, 1893 



PHASES IN THE METAMORPHISM OF THE SCHISTS OF 

 SOUTHERN BERKSHIRE* 



BY WILLIAM H. HOBBS 



{Read before the Society August 16, 1892) 

 CONTENTS 



Page 



Introduction 167 



Beds represented within the Area 167 



Evidences of orographic Disturbances 168 



Porphyritic Minerals of the Schists resulting from metamorphic Action 169 



The Minerals and their Association 169 



Porphyritic Feldspar 169 



Granophyre Structure in Feldspar 170 



Its Origin 171 



Secondary Enlargements of Feldspar 171 



Their Origin 173 



Garnet and its secondary Enlargements 173 



Staurolite 174 



Reactionary Rims of Staurolite and Magnetite about Garnet 174 



Tourmaline and its secondary Enlargement 175 



Porphyritic Biotite 176 



Ottrelite. 176 



Summary and Conclusions 177 



Introduction. 



Beds represented within the Area. — In southwestern Berkshire county, 

 Massachusetts, and in northwestern Litchfield county, Connecticut, is an 

 area in which non-calcareous schistose rocks alternate with limestones 

 which are in part micaceous, dolomitic, graphitic, pyroxenic, tremolitic 

 or quartzitic.f Though the schists are the "mountain rock," they are 

 found in the valleys as well and are frequently inclosed as islands in 



* Published with the permission of the Director of the United States Geological Survey. 



fThe area has been described and mapped by Professor J. D. Dana : On Taconic Rocks and Strat- 

 igraphy, with a Geological Map of the Taconic Region. Am. Jour. Sci., 3d ser., vol. xxix, pp. '205- 

 ■i-ii, pp. 4;;7-M3, pl. ii. 



XXV— Bum,. Geol. Soc. Am., Vol. 4, 1892. (167) 



