WOCKNAL OF GEOLOGY 
MARCH-APRIL, 1909 
PVOVUION (OF --hARLY ~PALHOZOIC FAUNAS. IN 
RELATION £O) THEIR ENVIRONMENT? 
CHARLES D. WALCOTT 
Ill 
CONTENTS 
Introduction. 
North American Continent at the Beginning and at the Close of Cambrian Time. 
Life at the Beginning of Known Cambrian Time. 
Distribution of the Lower Cambrian (Olenellus) Fauna over the North American 
Continental Platform of Cambrian Time. 
Conditions in Middle and Upper Cambrian Time. 
Evolution of Faunas. 
INTRODUCTION 
The evolution of early Paleozoic faunas could be treated with far 
greater effectiveness if the studies now in progress on the Cambrian 
faunas were nearer completion. ‘That of the brachiopods is well 
advanced? but the great collections of the U.S. National Museum, 
representing the crustacea and other invertebrates, have not been 
studied as to their mode of occurrence, geographic distribution, and 
biologic and environmental relations. Only a brief summary of the 
known evidence afforded by the Cambrian rocks and faunas of North 
America is considered in this paper. 
Animals and plants, as now known, are profoundly influenced by 
« Read before Section E of the American Association for the Advancement of 
Science, Baltimore meeting, December, 1908. : 
% Smithsonian Miscellaneous Collections, Vol. LIII, No. 4, 1908, pp. 139-65. 
Vol. XVI, No. 3 193 
a 
