326 PROCEEDINGS OF THE AMERICAN ACADEMY. 



now, the northward shore current may have swung pretty well around 

 the mainland, as sketched in line ABH. But as the east side of the 

 Cape was cut away and straightened, and as the shore current grew 

 stronger and stronger, it became increasingly difficult for the waters to 

 turn the curve that led to High head ; and at last, when the turning 

 was impossible, the spit began to form on the line FjE. As the 

 change progresses, the current swings on a fulcrum, F'., ; the spit 

 broadens by the external addition of new bars, FgG, as well as by the 

 formation of sand dunes inside of the curve ; and the fulcrum shifts 

 along the shore to the northwest, as indicated by the points F^, F3, 

 Figure 6, in the manner already explained for Figure 5. 



The important point to note is tluit here^ just as on the New Jersey 

 coast, the grading of the initial irregular shore line into a curved cliff 

 shore, and the straightening of the curved cliff" shoi'e enough to require 

 the growth of the tangent bar, must have been accomplished early in 

 the development of so weak a land mass as Cape Cod in face of waves 

 80 strong as those of the Atlantic. 



Dimensions of the Original Cape. 



Now inasmuch as no very long time can have been required for the 

 Atlantic waves to wear back the original shore line of the Cape to a 

 graded outline, ABH, of which the High head cliff is a part, and 

 inasmuch as the growth of the springing spit must have been begun 

 soon after the grading of the shore, it follows that the original con- 

 structional outline of the land in front of the High head cliff cannot 

 have extended far into the sea. I have given it an extension of 3,000 

 feet in Figure 1. A similar original extension of all the mainland of 

 the Cape may be assumed outside of the graded shore line ABH, 

 that existed before the springing spit was formed ; and thus the origi- 

 nal outline of the eastern side of the mainland has been roughly 

 sketched in. As drawn in Figure 1, the greatest retreat from the 

 original shore to the present shore is nearly two and a half miles, and 

 at the present strength of wave action, 3,000 or 4,000 years may be 

 roughly taken to have sufficed for the accomplishment of this change. 

 This time is probably too long rather than too short, for the retreat 

 now must be slower than when the cliff" was lower. 



It should be carefully understood that the period here computed 

 does not measure postglacial time ; for, as already stated, it is believed 

 that the land hereabouts stood somewhat higher than now during the 

 accumulation of the stratified sands, and that only after the time of 



