ORIGIN OF FOLIATION IN THE PRE-CAMBRIAN ROCKS 

 OF NORTHERN NEW YORK 1 



WILLIAM J. MILLER 



Northampton, Massachusetts 



INTRODUCTION 



Data bearing upon the problem of the origin of foliation in the 

 pre-Cambrian rocks of northern New York have been gathered dur- 

 ing the last ten years by the writer while he was engaged in the 

 geological surveys of various quadrangles in the Adirondack 

 Mountain region. In the attempt to explain the origin of the 

 foliated structures of the rocks, examples and analogies from other 

 parts of the world will be introduced, and it is hoped that the con- 

 clusions reached may have a wider application than to the Adiron- 

 dack region alone. 



This paper is not much concerned with criteria for the deter- 

 mination of original igneous or sedimentary character of the rocks. 

 The conclusions reached are almost wholly based upon observations 

 made upon rocks which have been generally recognized as quite 

 certainly either igneous or sedimentary. Rocks of rather doubtful 

 origin are frequently met in minor quantity, but these may be 

 disregarded in the present discussion. 



The strata all belong to the very ancient Grenville series, includ- 

 ing various gneisses and schists, together with crystalline limestone 

 and quartzite. The chief criteria for the determination of their 

 sedimentary origin are: distinct banded structures, often showing 

 alternating layers of widely different composition sharply separated 

 from each other; presence of extensive bodies of limestone and 

 quartzite interbedded with the gneisses; dissemination of graphite 

 flakes through many of the rocks ; and the very common occurrence 

 of garnet in many of the rocks, and the less common occurrence 

 of sillimanite. 



1 Published by permission of the Director of the New York State Museum. 



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