312 PROCEEDINGS OF THE AMERICAN ACADEMY, 



lation of this northeast bar to the peninsula of Provinceland, and from 

 the relation of the peninsula to the western bar, that a somewhat 

 shorter time was allowed for cutting the north cliff of High head than 

 for cutting its west cliff ; but inasmuch as wave energy was greater on 

 the north than on the west, time and energy varied inversely, and hence 

 about the same amount of lost land may be added to each cliff. The 

 amount of reduction suffered on either side of High head is therefore 

 roughly proportional to the time before the bar was built in front of 

 the north cliff. 



The north bar, BJ, that for this reason takes our attention, is one 

 of the class built by marine action, as recognized by Admiral Davis. 

 It springs tangent to the curve of the long convex cliff and beach, NB, 

 on the east side or '"back '"' of the Cape. As tiie retreat of the margin 

 of High head is measured by the time befoi'e the north bar was built, 

 the question arises whether bars of this kind are built in front of 

 straight cliffs early or late in the attack made by the sea on the land. 

 This question may be divided into two ; the first considering the de- 

 velopment of the cliff; the second considering the stage in the devel- 

 opment of the cliff when the protecting bar would be likely to grow 

 out in front of it. 



Development of Shore Profiles. 



Let the activities of the sea be resolved into two components ; one 

 acting on and off shore; the other along shore; and let the effects of 

 the first of these components be now examined alone, postponing con- 

 sideration of the effects of the second component to the next section. 



On some young coasts, the on-and-off-shore movements of the sea 

 carry out to deep water all of the waste that is abraded from the land 

 and its submarine slope, leaving the shore line bare.* The rocky 

 floor seen at low tide on the coast of Brittany illustrates this condi- 

 tion. Here the sea is able to do more work than it has to do. Its 

 action is like that of a young river, whose ability to carry load is 

 greater than the resistance of the load that it has to carry, and whose 

 valley floor is therefore attacked and deepened. But as the valley is 

 deepened, the slope, velocity, and carrying power of the river are all 

 decreased ; at the same time the load, derived chiefly from the val- 

 ley slopes, is increased : thus ability to do work gradually falls into 



* The problem of flat coasts, with shallow off-shore waters, is so different 

 from the problem here considered that it will be treated independently in a later 

 section. 



