Page:Walcott Cambrian Geology and Paleontology II.djvu/17

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CAMBRIAN GEOLOGY AND PALEONTOLOGY

II

ABRUPT APPEARANCE OF THE CAMBRIAN FAUNA ON
THE NORTH AMERICAN CONTINENT[1]

By CHARLES D. WALCOTT

(With One Map)


CONTENTS

PAGE
Introduction 1
Pre-Cambrian rocks 3
Sources of sediments 5
Origin of later Algonkian rocks 6
Pre-Cambrian Continental Surface 9
Unconformity between Cambrian and pre-Cambrian 11
Extent of withdrawal of Seas in Late Algonkian Time 12
Evidence of Fossils 13
Résumé 14
Bibliography 15

ILLUSTRATIONS

Plate 1. Map showing distribution of pre-Cambrian Rocks 4
Fig. 1. Theoretical profile of North American continent during later part of Algonkian time 10


INTRODUCTION

In accepting the invitation of the Representatives for Paleontology of the Swedish Committee of the Eleventh International Geological Congress, to take part in the discussion of "The Abrupt Appearance of the Cambrian Fauna," I decided to confine the geological discussion mainly to phenomena observed on the North American Continent and to limit paleontological conclusions to results obtained from studies of material from the oldest fossiliferous Cambrian rocks.

In summing up the Lower Cambrian fauna in 1891 [Walcott,


  1. Read at the Eleventh International Geological Congress, Stockholm, Sweden, August 18, 1910.

Smithsonian Miscellaneous Collections Vol. 57, No. 1