308 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Review of Previous Writings. 



The structures of the " mainland " of Truro and of the peninsula of 

 Provinceland are so unlike that their different origins have long been 

 recognized ; the former being attributed chiefly to diluvial or glacial 

 and aqueo-glacial agencies, the latter to marine agencies acting on the 

 former. The general character of existing processes by which the 

 shores are undergoing change, and the present rate of action of these 

 processes have been carefully examined by various observers ; but no 

 systematic attempt has been made to trace the processes and the changes 

 that they have produced backward to their beginning. This task is 

 therefore attempted here. 



Reconstruction of the Original Outline of the Cape. 



The development of the existing outline of Cape Cod must be traced 

 backward to the original outline. The initial form that it had before 

 the present cycle of cutting and filling began along its shores may be 

 roughly reconstructed by reversing the marine processes now at work 

 and following them until they lead back through earlier and earlier 

 conditions. The restoration may be regarded as complete, when the 

 reconstructed forms are everywhere of non-marine origin. Then, re- 

 versing the order of study, the normal operation of cutting and filling 

 processes should lead forward again to the existing outline of the Cape, 

 and should even allow a reasonable prediction of future changes for 

 some time to come. 



Provinceland, the Chatham bars, and Monomoy, and a few small 

 bars near Wellfleet, must first be removed, as they consist wholly of 

 sea-carried materials, their arrangement being closely accordant with 

 action at present sea level. The tidal marshes north of Wellfleet, 

 along Paraet river, and elsewhere, should be excavated. The '' main- 

 land," chiefly of glacial and aqueo-glacial deposits, will then stand out 

 alone, as indicated by the outline NBHQPTC, Figure 1. It descends 

 to the shore on nearly all sides in steep cliffs of moderate height ; long, 

 straight, or gently curving beaches running along the base of the cliffs. 

 Exceptions to this rule are found almost exclusively on the shores 

 of protected bays, such as those north of Chatham and about Well- 

 fleet. The cliffed descent of the mainland to the smooth beaches is 

 manifestly an indication of destructional retreat from a formerly greater 

 extension seaward, just as the gentle slope of the land to the irregular 

 shore line of the bays is an indication of small change from construc- 

 tional form. 



