CONTENTS. xvil 



PAGE 



The Upper Cambrian 225 



Sections of the Cambrian and their Interpretation 225 



Interpretations 229 



How far may gradation have been competent to bring 

 about the submergence of the continent? 231. How far 

 may superficial deformation have contributed to the 

 submergence of the lands? 233. Lateral spreading, 233. 

 Mutual adjustment of continental and oceanic segments, 

 235. Isostatic adjustments due to gradation, 236. 

 Adjustments due to thermal changes resulting from gra- 

 dation, 237. Adjustments due to thermal changes inci- 

 dent to diastrophism, 237. Adjustments due to easing 

 of stresses, 237. 



Basis for the Subdivision of the Cambrian 238 



Stratigraphic relations, 238. Fossils, 239. Sequence 

 of faunas based on stratigraphy, 242. Upper limit of the 

 Cambrian system, 243. 



Sedimentation in the Cambrian Period 246 



Sources and kinds of sediments, 246. Geographic 

 variations in the sediments, 247. Variation in a given 

 locality, 250. 

 Distribution, Thickness, and Outcrops of the Cambrian System 252 

 Position of outcrops, 253. Width of outcrops, 256. 

 Thickness, 257. 



Infirm Deductions from Thickness 257 



Selected Sections of the Cambrian 263 



Section in southeastern Newfoundland, 264. Section 

 in western Vermont, 265. Section in Massachusetts, 265. 

 Section in northern New Jersey, 266. 



Summary of Physical Events and Interpretations 266 



Changes in the Cambrian Sediments since their Deposition 267 



Close of the Cambrian 269 



Foreign Cambrian 269 



Europe, 269. Other countries, 272. 



Duration of the Cambrian Period \ . . . . 273 



The Life of the Cambrian 276 



The first fair record, 276. What stage of evolution is rep- 

 resented? 276. The scantiness of plant fossils, 278. 



The Animal Fossils 279 



Arthropoda, 280. Mollusca, 283. Molluscoidea, 284. 

 Vermes, 286. Echinodermata, 286. Coelenterata, 286. 



