552 DTJisrES OF amekican coasts. 



servation of its structure. There are sandstones, such, for example, 

 as are used for grmdstones, where the grit, as it is called, is of ex- 

 ceeding sharpness ; others where the angles of the grains are so 

 obtuse that they scarcely act at all on hard metals. The former may 

 be composed of grains of rock, disintegrated indeed, and re- 

 cemented together, but not, in the meanwhile, much rolled ; the 

 latter, of sands long washed by the sea, and drifted by land-winds. 

 There is, indeed, so much resemblance between the effects of 

 driving winds and of rolling water upon light bodies, that there 

 might be difficulty in distinguishing them ; but after all, it is not 

 probable that sandstone, composed of grains thrown up from the 

 salt sea and long tossed by the winds, would be identical in its 

 structure with that formed from fragments of rock crushed by 

 mechanical force, or disintegrated by heat, and again agglutinated 

 without much exposure to the action of moving water. 



Dunes of Americcm Coasts. 



Upon the Atlantic coast of the United States, the prevalence of 

 western or off-shore winds is unfavorable to the formation of 

 dunes, and, though marine currents lodge vast quantities of sand 

 in the form of banks on that coast, its shores are proportionally 

 more free from sand-hills than some others of lesser extent. There 

 are, however, very important exceptions. The action of the tide 

 throws much sand upon some points of the New England coast, 

 as well as upon the beaches of Long Island and other more south- 

 ern shores, and here dunes resembling those of Europe are formed. 

 There are also extensive ranges of dunes on the Pacific coast of 

 the United States, and at San Francisco they border some of the 

 streets of the city. 



The dunes of America are far older than her civilization, and 

 the soil they threaten or protect possesses, in general, too little 

 value to justify any great expenditure in measures for arresting 

 their progress or preventing their destruction. Hence, great as 

 is their extent and their geographical importance, they have, at 

 present, no such intimate relations to human life as to render them 

 objects of special interest in the point of view I am taking, and 

 I do not know that the laws of their formation and motion have 

 been made a subject of original investigation by any American 

 observer. 



