DAVIS. — OUTLINE OF CAPE COD. 



319 



to the northwest. The problem is to determine at what stage in the 

 history of a clifFed shore line such a bar or spit might grow out from 

 one part of its face and protect another part. 



Off-shore Bars. 



In order to avoid misapprehension, it is advisable to make careful 

 distinction between those bars or spits which spring as tangent attach- 

 ments to a clifFed shore, often extending into comparatively deep 

 water, and those off-shore bars which are built up from the bottom in 

 shallow water, not immediately connected with the mainland. Exam- 



MAINLAND 



CM L MB 



SE^ 



^^^^. 



b' s b" 



pies of the latter class are common along a great extent of our southern 

 coast, especially where the tides are weak. Briefly stated, their his- 

 tory seems to be as follows. When waves roll in upon a shelving 

 shore, as in Figure 4, much of their energy is expended on the bottom. 

 Between the line of their first action far off shore and their final ex- 

 haustion on the coast, C, there must be somewhere a zone of maximum 

 action. This zone must lie farther seaward when large storm waves 

 roll in than when the sea is slightly ruffled in fair weather. Let the 

 zone of maximum action for storm waves be shown by Z in profile. 

 Here the bottom is deepened; the coarser particles are moved land- 

 ward, forming a shoal and in time a bar, B', enclosing a lagoon, L; while 



