In a " Memoir upon the Geological Action of the Tidal and other Currents of the 

 Ocean," pul^lished in the fourth volume (New Series) of the Memoirs of the Ame- 

 rican Academy of Arts and Sciences, I endeavored to trace a permanent and intel- 

 ligible connection between the currents of the sea and the alluvial deposits on its 

 l)orders, and in its depths ; to show in what manner the structure, position, and 

 amount of these deposits depended on this connection ; and, finally, to assign to it 

 the character of a law, subordinate to the higher law of universal gravitation, which 

 had, by a consistent and uniform operation, combined with other laws to give to the 

 great masses of land, called continents, their actual form and body. 



The views contained in this Memoir were founded upon observation. An exami- 

 nation of the various parts of the alluvial coast of the United States, through a 

 series of years, had led to the discovery that the shape, extent, and distribution, of 

 the loose material of which they are composed, — quartzose sand, — were chiefly deter- 

 mined by the action of the tides. It was seen that the same forms of deposit were 

 constantly repeated under similar circumstances ; and the conclusion was therefore 

 drawn, that the forms and circumstances were mutually dependent. 



This being the case, we are enabled to explain the character of the present forma- 

 tions on alluvial coasts ; to account for their peculiar shape, and their comparative 

 size ; to understand the law of their accumulation, or growth, and to foresee the 

 future results of certain combinations of circumstances, by a study of similar in- 

 stances elsewhere. 



One of the first steps in the Memoir referred to, was to specify the different kinds 

 of deposit that are found below and above the surface of, the sea. They were clas- 

 sified under the name of shoals, hooks, bay deposits, bars, beaches, &c. ; and their 

 characteristic features being descrilaed, the precise and distinct mode of operation of 

 the current, by means of which these features were decided, was stated and illus- 

 trated by numerous examples. 



The next inquiry was concerning the geographical distribution of these alluvial 

 deposits in all parts of the world. The cases of ocean deposits hitherto adduced, 

 were those of the American shores, and principally of the shores of New England. 

 They were accessible ; they exhiliited in minute detail all the different results of 

 constructive action, and had been maturely examined and collated. They furnished 

 also the examples for illustration, as they had first suggested the principles to be 

 elucidated. But leaving these districts, the generaUzation of the views presented, 

 was extended so as to become applicable to the sandy coast of the United States, 



