﻿II. 



A Memoir upon the Geological Action of the Tidal and other Currents of the Ocean. 

 By CHARLES HENRY DAVIS, A. M., A. A. S., etc. 



LIEUTENANT U. S. NAVY. 



(Communicated to the Academy, November 8th, 1848.) 



The views presented in the following memoir are derived from a study of the tidal 

 currents on our northern and northeastern shores for the last six years, during which 

 time I have taken part, as hydrographical assistant, in the survey of the coast of the 

 United States, conducted under the able superintendence of Professor A. D. Bache. 



This portion of our coast abounds in alluvial and subaqueous deposits, the most 

 numerous, and perhaps the most striking, examples of which occur on and about the 

 island of Nantucket. It is particularly in the survey of this district that I have been led 

 to trace the connection between the currents and the shoal formations which give a 

 peculiar character to its navigation. The changes that are supposed to take place in 

 these shoals are the subject of popular inquiry, and this inquiry could only be satisfactorily 

 answered by an investigation into their mode of formation, and the probable causes that 

 determine their shape and locality. 



Having arrived at some definite views concerning the relation of the currents in this 

 immediate vicinity to the deposits below the surface, and to those that have been raised 

 above the water by the transporting power of the winds, such as hooks, beaches, &c, 

 it was an easy and natural step, first, to extend the reasoning suggested by these humble 

 instances to the more grand subaqueous and alluvial deposits at a distance from this con- 

 tinent, on the shores of Europe, and elsewhere ; and afterwards, remembering that the 

 laws of nature are constant, uniform, and universal, to consider how far the same modes 

 of operation have been employed, in previous geological periods, in distributing or collect- 

 ing the loose materials of the earth's surface. 



Whilst occupied with these inquiries, it was my good fortune to have with me, as a 

 guest, Mr. Edward Desor, a gentleman too well known in the world of science to need 



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