﻿138 GEOLOGICAL ACTION OF 



Section III. — Geographical Distribution. 



The preceding pages of this memoir have been devoted to a description of the 

 various forms of ocean deposit, and to a statement of the mode of connection between 

 those forms and the tidal currents from which they are derived. Hitherto I have con- 

 fined my inquiries to the shores of the United States, and particularly to the coast of 

 New England, because there the various results of constructive and destructive action 

 were under immediate observation, the nature of the tidal currents was well known, and 

 local information concerning recent changes has been most readily obtained. The next 

 step is the application of the natural laws deducible from these investigations to similar 

 formations on this continent and in other parts of the world. Before entering, how- 

 ever, into the subject of geographical distribution, it is necessary to lay down one prin- 

 ciple of tidal deposit which has not yet been distinctly enunciated. It is this, that 

 deposits upon the ocean border are only made by the current of the flood tide. 



In the sounds and bays, the ebb tide may also leave its burden, since in its retreat it 

 may not only meet with obstructions, but must press upon the land, in some parts, pre- 

 cisely as the advancing flood does upon the exterior coast. In a group like the Nan- 

 tucket Shoals, the ebb, carrying with it the sand that has been loosened on the shore, and 

 bein"- hindered in its course by the inequalities of the bottom, must also contribute- 

 to build up the deposits. These cases are not alleged as exceptions to a law, but are 

 stated as modifications merely, through which the action of the ebb is brought to resem- 

 ble that of the flood. In general, as the deposit of the flood is made on the shore in 

 the direction of its progress, so the deposit of the ebb is buried in the bosom of the 

 ocean. The former furnishes the material for the alluvial deposit above water; the 

 latter supplies the substances found in the depths of the sea. 



It is not meant to say by this, that the action of the flood and ebb tides is reciprocal. 

 On the contrary, the mode of operation of the flood is essentially cumulative. Its ten- 

 dency, also, is to continually carry onward the deposit, in the course of its current, so that 

 it performs the double office of increasing the collection at every successive tide, and of 

 advancing from place to place the matter at its disposal. This double process is exemplified 

 by the manner in which the materials of wrecks are conveyed along the shore in the direc- 

 tion of the flood at that place. I have previously said, that the course of the flood current 

 on the outside of the island of Nantucket is from west to east on the south shore, and 

 turning with the trend of the land from south to north on the east shore. A few 

 years since, the British bark The Earl of Eglintoun was wrecked on the south 

 side of the island of Nantucket, two miles east of the meridian of the town. Her 



