46 SEA AND LAND 



sheltered place, will commonly be destroyed within a mile of 

 the point where they were first exposed to the surf action. 

 On the eastern face of Cape Ann, where exceedingly hard 

 fragments of granite — the waste rock from the quarries — 

 have been cast into the sea, it requires several years for a 

 frae-ment the size of a nail-keir to be rounded into the sphe- 

 roidal form so characteristic of marine erosion. Slow as this 

 wearing may seem, we must remember that, measured against 

 the geologic ages, it is indeed exceedingly swift. 



It will readily be seen that a portion of the beach, that 

 which is above the limit of the sea except in times of high 

 tide and great storms, rises more steeply than the portion 

 which is below the sweep of the water; in fact, the line from 

 the shallow water to the crest of the beach is like one-half 

 of a catenary curve, or the shape in which a chain or rope 

 hanfi-s when it is suspended between two elevated points. 

 Such a curve is, as we easily recall, nearly Hat in the middle 

 and rises steeply near the support. This shapely form is due 

 to the action of the waves, which continually thrust or heave 

 the sand and gra\-cl against the shore. The effect of this 

 urgence is modified by the continued reflux of the waves ; in 

 their backward movement they carr>- away the greater part 

 of what the)- have brought in. In a short time an equation 

 is determined between the incoming and outgoing of the 

 detritus, and so the sea-shores of all the world establish the 

 same rate of slope for like conditions. In times of storm 

 the slope may. for a little while, be brought to a greater 

 declivity, but the weaves, moderating in violence, proceed to 

 drag away a part of the detritus and soon restore the 

 declivity to its normal condition. 



When a storm has blown obliquely upon the shore, so that 



