CONTENTS. 
Page. 
Letter of transmittal ■ « . 11 
Introduction 13 
Chapter I. An account of geological surveys in the South Mountain below 
the Susquehanna 14 
Historical review 11 
Bibliograp 1, 19 
Chapter II. Geological relationship of the rocks of the Monterey district- ... 20 
General description of the area studied 20 
Extent and character of the three rock types 20 
Sedimentary rocks 21 
Areal distribution 21 
Structural features 21 
Thickness 21 
Age and superposition 21 
Acid eruptives 23 
Areal distribution 23 
Character 23 
Previous descriptions 23 
Economic value 24 
Basic eruptives 24 
Areal distribution 24 
Character 24 
Previous descriptions 25 
Ore deposits of the Monterey district 25 
Comparative age of sedimentary and igneous rocks 27 
Contacts described 27 
Conclusions 28 
Comparative age of acid and basic eruptives 29 
Field relations 29 
Probable explanation 29 
Summary 30 
Chapter III. Petrographical description of the Cambrian rocks 31 
Macroscopical description 31 
Microscopical description 31 
Quartzite 31 
Slates 33 
Chemical analysis „ 33 
Summary 34 
Chapter IV. Petrographical description of the acid eruptives 35 
Nomenclature 35 
Quartz-porphyries 39 
Distribution 39 
Macroscopical description 39 
Microscopical description 39 
Phenocrysts 39 
Feldspar 39 
Quartz 40 
5 
