CONTENTS. 



Chapter I.' — Introduction 11 



Previous work in the district 13 



Mode of Vfovk 22 



Magnetic observations 24 



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



Geograpliical limits 25 



Structure and stratigrapliy 25 



Physiography 29 



Topography 29 



Drainage - 31 



Timber and soil 36 



Chapter III. — The Archean 38 



Distribution, exposures, aud topography 38 



Eelations to overlying formations 39 



Petrographical characters 40 



Biotite-granite (granitite) 40 



Gneissoid biotite-granite, border facies of granite 43 



Acid dikes in Archean 45 



Basic dikes in Archean 46 



Schistose dikes 46 



Massive dikes 48 



E^sum6 49 



Chapter IV. — The Lower Huronian series 50 



Section 1. — The Randville 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 aud 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 clays 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 



3 



