

CONTENTS. 



Pase. 



Letter op transmittal ^^ 



introduction, by charles elchard van hise ->^vii 



Outline of monograph - xxix 



Part I.— The western part of the Crystal Falls district, by J. Morgan Clements. H 



Chapter I.— Introduction ^^ 



Previous work in the district 1'^ 



Mode of work 



Magnetic observations -'* 



Chapter II.— Geographical limits, structure and stratigraphy, and physiography 25 



Geograpliioal limits ^^ 



Structure and stratigraphy -5 



Physiography ^'^ 



Topography. 

 Drainage 



Timber and soil ''" 



Chapter III.— The Archban 38 



Distribution, exposures, and topography 3° 



Relations to overlying formations * 39 



Petrographical characters *'' 



Biotite-granite (grauitite) ^^ 



Gneissold biotite-granite, border facies of granite 43 



Acid dikes in Archean 45 



Basic dikes in Archean 46 



Schistose dikes 46 



Massive dikes 



R^sum^ 



49 



Chapter IV.— The Lower Hcronian series 50 



Section 1. — The Eaudville dolomite 50 



Distribution, exposures, and topography 50 



Petrographical characters - 51 



Relations to underlying and overlying formations 53 



Thickness - 53 



Section 2.— The Mansfield slate 54 



Distribution, exposures, and topography 54 



Possible continuation of the Mansfield slate 55 



Petrographical characters - - - 56 



Gray wacke . 



56 



Clay slate and phyllite 57 



Origin of clay slate and phyllite 58 



Present composition necessarily different from that of rock from which derived 58 



Analysis of Mansfield slate 59 



Comments on analysis - 59 



Comparison of analysis of Mansfield clay slate with analyses of clay s 60 



Comparison of analysis of Mansfield clay slate with analyses of other clay slates. .. 61 



Siderite-slate, chert, ferruginous chert, and iron ores 62 



Relations of siderite-slate, ferruginous chert, and ore bodies to clay slate 63 



Relations of Mansfield slate to adjacent formations 63 



Relations to intrusives 



63 



Relations to volcanics 64 



