in the Pleistocene and Post-Pie isioeene. 11 



shore lines represent therefore the rhythmic rise of the sea 

 upon a land surface previously dissected by subaerial erosion. 

 The baseleveling on the softer rocks near the larger streams 

 each time during the emergent phase had reached to an 

 advanced stage, but upon the broad formations of harder rocks 

 it had not progressed beyond the stage of youth. The sub- 

 mergent phase, however, lasted long enough for the sea to 

 produce notable planation against the outstanding harder 

 masses. Subaerial baseleveling at these stages seems also to 

 have made notable progress, marking times of diastrophic rest. 

 The submergence was in each cycle great enough to permit 

 concentration of marine erosion against the headlands, the 

 waves not spending their force upon the bottom. The motion 

 of the sea-level was therefore cyclic, but not smoothly undula- 

 tory. If time be laid off as a horizontal axis, the curve of sea- 

 level was nearer to the form of the common cyloid than to the 

 sinusoid. The variety of the cyloidal curve suggested ap- 

 proaches that described by a point on the circumference of a 

 rolling wheel. This curve is characterized by a nearly flat top 

 and a cuspate bottom. Conceive the point to be somewhat 

 within the wheel and the pointed bottom of the curve would 

 be somewhat broadened out. Conceive the wheel further- 

 more to be rolling down an irregular grade. Such a more 

 complicated curve as would now be generated by the motion 

 of the point may be nearer to the actual record of the sea-level 

 movements against the Atlantic shore. It does not quite rep- 

 resent the discontinuous nature of the movements, but it does 

 make graphic the conclusion that the emergent phases of the 

 oscillations are relatively rapid and brief, the submergent 

 phase prolonged, and marked by a slowly rising level of the 

 sea. The retreats of the sea are thought to have been more 

 rapid than the advances. 



In Maryland broad and gently sloping terraces of Pleisto- 

 cene age face the sea, bounded on the land side by low escarp- 

 ments. They mark submergent phases of rhythmic crnstal 

 movements and show planation at levels of 220, 100 and 40 

 feet respectively, in descending order of age. The gentle sea- 

 ward slopes are more or less in adjustment with the slope of 

 the subaqueous profile of wave-worked bottoms. Within the 

 valleys the deposits are regarded as fluviatile. Facing the sea 

 they are doubtless marine, though the porous nature of the 

 thin mantle of deposits has not permitted the preservation of 

 marine fossils. The terrestrial fossils fix the age as Pleisto- 

 cene. The oldest and highest deposits are known as the Sun- 

 derland formation, and are apparently of early Pleistocene age. 

 The youngest, known as the Talbot, are judged to be late 

 Pleistocene. The materials of all three, Sunderland, Wicomico, 



