506 W. B. Clark — Brandywine Formation. 



rapidly earned. Although fluviatile deposition may have 

 actually taken place over part of the area during the period of 

 subsidence it must have been replaced ultimately by off-shore 

 deposition as the sea transgressed. In no other way can the 

 form and structure of the formation be fully interpreted. 



Age of the formation. — There has been much discussion of 

 the age of the deposits composing the Brandywine formation, 

 but as no determinable fossils have hitherto been found in the 

 beds no definite conclusions have been reached. It has been 

 generally accepted that the post-Brandywine deposits are of 

 Pleistocene age, while the Brandywine formation itself has 

 been questionably referred by most authors to the Pliocene on 

 the ground of the more extensive erosion to which the strata 

 have been subjected and the greater decay of the constituent 

 materials. The author raises the question, however, whether 

 the Brandywine formation might not with entire propriety be 

 referred to the early Pleistocene, all of the surficial terrace 

 deposits therefore of the Middle Atlantic Coastal Plain being 

 placed in that event within the limits of the Pleistocene. 



Geological Laboratory, Johns Hopkins University, Baltimore, Md. 



