PALEOGEOGRAPHIC MAPS OF NORTH AMERICA^ 

 I AND 2. EARLY CAMBRIAN AND LATE CAMBRIAN^ 



BAILEY WILLIS 

 U. S. Geological Survey 



At the Baltimore Meeting of the American Association for the 

 Advancement of Science a number of paleogeographic maps of 

 North America, representing the continent at intervals from Cam- 

 brian to Quaternary, were exhibited. They had been prepared in 

 collaboration with some of the geologists who presented papers 

 in the symposium on correlation, and to a certain extent they serve 

 to illustrate the changing geologic conditions which form a factor 

 in the problems of correlation. I have been requested to publish 

 them in connection with the correlation papers in the Journal of 

 Geology, and am glad to do so, although it is not practicable to 

 present a discussion of the particular facts which have been considered 

 in the construction of each individual map. 



In general the lines of evidence have been considered somewhat 

 in the following manner. 



A certain period having been selected as that which should be 

 mapped, the epicontinental strata pertaining to that time interval 

 have been delineated. The phenomena of sedimentation and erosion 

 have then been correlated, with a view to determining the sources 

 of sediment and topographic conditions of land areas, and from these 

 data the probable positions of lands have been more or less definitely 

 inferred. Thus, certain areas within the continental margin are 

 distinguished as land or sea, and these areas may be defined as 

 separate bodies or connected according to inferences based upon 

 isolated occurrences or upon later effects of erosion. 



It is assumed that the great oceanic basins and such deeps as the 

 Gulf of Mexico and the Caribbean have been permanent features 

 of the earth's surface at least since some time in the pre-Cambrian. 

 These deeps can thus be placed upon the map and their connection 

 with the epicontinental seas may be tentatively established. 



1 Published by permission of the Director of the U. S. Geological Survey. 



2 Based largely on data furnished by C. D. Walcott. 



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