56 THE BOTTOM OF THE SEA. 



littoral deposits are, therefore, of comparatively 

 slight amount when regarded as to their quantity 

 merely, but theoretically they are of the greatest 

 importance. An exact knowledge of their character 

 often enables the physicist to determine the oscilla- 

 tions of the sea, how it has retired from the land or 

 encroached upon it, and consequently to what extent 

 the terrestrial crust has been affected. The follow- 

 ing details are borrowed from a work presented to 

 the French Institute, some two years ago, by M. 

 IJelesse, and which may be described as a complete 

 study of the deposits which are being formed in 

 our time upon the coasts of France, and of the re- 

 lations they bear to currents and marine animals, 

 but more particularly to the nature of the rocks 

 which form the shore. 



This littoral deposit presents a mineralogic com- 

 position of considerable variety at a level corres- 

 ponding to that of high-tide, because it includes the 

 debris of the neighbouring cliffs. At the level of 

 low tide, on the shores of the Ocean, it is much more 

 uniform, and even exhibits a constant character to a 

 great extent. Where we find this to be the case, we 

 may be sure that, whatever be the character of the 

 rocks which concur to form the deposit, the sea is 

 not slow to destroy them. The minerals we dis- 

 cover are those \\hich offer considerable resistance to 



