240 



EARTH FEATURES AND THEIR MEANING 



FIG. 262. Storm beach of coarse 

 shingle about four feet in height at 

 the base of Burnt Bluff on the north- 

 east shore of Green Bay, Lake 

 Michigan. 



forward slope graded by the shore current, but a steep back- 

 ward slope on the angle of repose. Most storm beaches have 

 been largely shaped by the last great storm, such as comes only 



at intervals of a number of years. 

 Bar, spit, and barrier. 

 Wherever the shore upon which 

 a beach is building makes a 

 sudden landward turn at the en- 

 trance to a bay, the shore cur- 

 rents, by virtue of their inertia 

 of motion, are unable longer to 

 follow the shore. The debris 

 which they carry is thus trans- 

 ported into deeper water in a 

 direction corresponding to a con- 

 tinuation of the shore just before 



the point of turning (see Fig. 259, p. 238). The result is the 

 formation of a bar, which rises to near the water surface and is ex- 

 tended across the entrance to the bay through continued growth 

 at its end, after the manner of constructing a railway embank- 

 ment across a valley. 



Over the deeper water near the bar the waves are at first not 

 generally halted and broken, as they are upon the shore, and so 

 the bar does not at once 

 build itself to the surface, 

 but remains an invisible 

 bar to navigation. From 

 its shoreward end, how- 

 ever, the waves of even 

 moderate storms are 

 broken, and the bar is 

 there built above the water 

 surface, where it appears 



as a narrow Cape of Sand , FIG> 263 . _ Spi t O f shingle on Au Train Island, 

 or shingle which gradually Lake Superior (after Gilbert). 



thins in approaching its 



apex. This feature is the well-known spit (Fig. 263) which, as it 

 grows across the entrance to the bay, becomes a barrier or barrier 

 beach (Fig. 264). 



