434 



HISTORICAL GEOLOGY 



FIG. 453. Supposed outline of North America early in the Tertiary 

 period. The dotted pattern represents deposits made on land. (Modi- 

 fied after Willis.) 



the beginning of the coastal plain. Some of these Tertiary 

 rocks are sand, peat, clay, and marl, and some are soft lime- 

 stone or chalk. They are interrupted by a number of slight 

 unconformities. In these deposits and unconformities we 

 find recorded the fact that the eastern and southern margin 



