CONTENTS xi 



CHAPTER XIV 

 THE ARCHEOZOIC ERA 



GENERAL 436 



Conceptions of the earth's composition, 436. General character- 

 istics of the Archean, 440. 



DISTRIBUTION AND LOCAL DEVELOPMENT OF ARCHEAN 443 



Bearing of the Archean on theories of the origin of the earth, 446. 

 Earlier views of the Archean, 446. Life during the Archeo- 

 zoic, 447. Duration of the Archeozoic, 447. Climate, 447. 



CHAPTER XV 

 THE PROTEROZOTC ERA 



FORMATIONS AND PHYSICAL HISTORY 448 



Stratigraphic relations, 448. Subdivisions, 450. Proterozoic 

 sedimentation, 450. Extent of Proterozoic formations, 453. 

 The exposed formations, 453. Geographic relations of the ex- 

 posed Proterozoic to the Archean, 455. 



PROTEROZOIC OF THE LAKE SUPERIOR REGION 456 



The Huronian systems, 457. The Keweenawan system, 460. 

 General considerations concerning the Lake Superior Protero- 

 zoic, 467. Sequence of events elsewhere, 470. 



PROTEROZIOC ROCKS IN OTHER REGIONS 471 



Cordilleran region, 472. Eastern part of the United States, 472. 

 Summary, 473. In other continents, 473. 



LIFE DURING THE PBOTEROZOIC ERA 473 



CLIMATE . . 474 



THE PALEOZOIC ERA 



CHAPTER XVI 



THE CAMBRIAN PERIOD 



FORMATIONS AND PHYSICAL HISTORY 476 



The subdivisions of the Cambrian and their distribution, 476. 

 Great submergence during the Cambrian, 478. Causes of sub- 

 mergence, 479. Basis for subdivision of the Cambrian, 481. 

 Sedimentation in the Cambrian period, 484. Distribution and 

 outcrops of the Cambrian system, 486. Cambrian in other 

 continents, 490. Duration of the Cambrian period, 493. 



