CONTENTS. xv 



PAGE 



III. The Modes of Deformation 123 



The thickness of the folded shell, 125. The shear- 

 zone, 126. Folding in tracts of least resistance, 127. 

 Periodicity, 128. Supposed combined action, 128. 

 The zone of accommodation, 130. The shear-zone a 

 zone of foliation, 130. The relations of the shear- 

 zone to igneous intrusions, 130. Secondary or tensional 

 movements, 131. Horsts, rift-valleys, etc., 131. Re- 

 lations to sedimentation, 132. 



CHAPTER III. 



THE ARCHEOZOIC ERA. 



The oldest accessible formation, 135. Delimi- 

 tations, 138. 



General Characteristics of the Archean 140 



Subdivision, 140. The great schist series, 142. 

 The great granitoid series (Laurentian) , 142. Similar 

 formations not Archean, 143. A special characteristic 

 feature, 143. The dias trophism of the Archeozoic era, 

 144. Metamorphism, 144. 



Distribution and Local Development 145 



General distribution, 145. In North America, 146. 

 Local development, 147. Bearing of the Archean on 

 the theory of the origin of the earth, 155. 



Earlier Views Concerning the Archean . 156 



The Archean in Other Countries 158 



Life During the Archeozoic Era 159 



Duration of the Archeozoic Era 160 



General Table of Geologic Divisions 160 



CHAPTER IV. 



THE PROTEROZOIC ERA. 



Stratigraphic Relations of the Proterozoic Rocks 163 



Subdivisions 165 



Proterozoic Sedimentation 166 



General considerations, 166. Extent; 168. The 

 sediments and their interpretation, 169. 

 Geographic Relations of the Exposed Proterozoic to the Ex- 

 posed Archean 171 



