66 SEA AND LAND 



doubtless orij^inally formed as shore-shelves near the old 

 lands, then elevated above the sea, folded into mountains, 

 and worn into hills, until we can no longer, or with difticulty, 

 recoL^nize their original aspect. 



If the relative level of the sea and land remained stead- 

 fast for a considerable geologic time, the detritus of a conti- 

 nental shelf would, und(;r the unceasing action of the tides, 

 and despite the perturbing effect of the waves in occasional 

 storms, grow steadfastly to the seaward ; but all our study of 

 the relations of sea and land tends to convince us that they 

 are peculiarly unstable. It seems likely that nowhere in the 

 world is the sea-margin at exactly the same height in any two 

 successive centuries. In general this variation is so slowly 

 brought about that in the brief moment of time for which we 

 have any account, in the case of the longest-known shores, we 

 do not have evidence of it, and the sea-level is said to be per- 

 manent. Again, it is sufficiently rapid to be observable in the 

 duration of a single human life. Thus on the coast of New 

 Jersey there is a tolerably rapid subsidence of the land, which 

 is sinking at the rate of near two feet in a century. Along 

 the shores from Eastport, southward, there have been many 

 ups and downs of the shore since the glacial period ; within 

 a range- of from a few score to a few hundred feet, the last 

 \-ariations appear generally to have lowered the shore in the 

 re'Mons south of New Brunswick. In those rei^ions where the 

 lat(M- movements of the coast-line have been of an uprising 

 nature, the effect is to brincf a ijreat deal of sand, which had 

 been in too deep water for the waves to afYect the particles, 

 within the power of the surges. In these cases the coast-line 

 becomes inundated with sand swept in from the sea. 



It is characteristic of the typical sandy shores, that their 



