12 CONTENTS 



PAGE 



THE GEOLOGY OF THE CRYSTALLINE ROCKS OF CECIL COUNTY. 



By F. Bascom 83 



Introductory 83 



Geographic and Geologic Relations 84 



Areal Distribution and Character of the Crystalline Formations. . ., . . 87 



Mica-Gneiss 88 



Igneous Intrusives 90 



The Granite-Gneiss 90 



Gabbro and Meta-Gabbro 92 



Meta-Pyroxenites and Meta-Peridotites 93 



Dike Rocks and other Intrusives in the Granite-Gneiss 97 



Intrusives in the Gabbro Belt 100 



Diabase Dikes 100 



Pegmatite Veins 101 



Structural Relations and Age of the Crystalline Formations 103 



The Mica-Gneiss 103 



The Eruptive Rocks 108 



Petrography of the Crystalline Formations 113 



Mica-Gneiss 113 



Granite-Gneiss 117 



Biotite-Granite (Quartz-Monzonite) 117 



Hornblende-Biotite-Granite (Quartz-Monzonite) 119 



Gabbro 121 



Meta-Gabbro or Quartz-Hornblende Gabbro and Hornblende 



Gabbro 121 



Norite and Hypersthene-Gabbro 125 



The Southern Gabbro Belt 128 



Non-Feldspathic Rocks 132 



Pyroxenite 132 



Peridotite 133 



Serpentine 134 



Dike Rocks 135 



Meta-Rhyolite 136 



Micro-Granitic Dikes 139 



Meta-Gabbro 140 



Diabase 140 



Summary 142 



Glossary of Geological Terms 143 



THE GEOLOGY OF THE COASTAL PLAIN FORMATIONS. By George 



Bureane: Shattitck 149 



Introductory 149 



The Potomac Group 151 



The Patuxent Formation 151 



The Patapsco Formation 153 



The Raritan Formation 155 



The Upper Cretaceous Formations 157 



The Matawan Formation 158 



The Monmouth Formation 159 



