PALEOGEOGRAPHIC MAPS OF NORTH AMERICA" 
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. 
When the distribution of lands and waters is thus inferentially 
1 Published by permission of the Director of the U. S. Geological Survey. 
203 
