SUBSIDENCE 69 



sand of sandy beaches or points should be sampled, 

 so as to ascertain how far it is formed by the breaking 

 down of the rock, and how far it consists of the re- 

 mains of organisms piled up by the waves. From the 

 inhabitants we often obtain valuable information, 

 positive measures of the loss or gain ; we frequently 

 require to learn from them whether we are examining 

 beaches which are permanent, or which shift according 

 to the variation of seasons or perchance the monsoons. 

 In the course of such work we may get indications 

 that land, formerly dry, has sunk below the sea ; 

 but this is more difficult to prove. The sea often cuts 

 a flat at the low-tide level into the land if the latter 

 be stationary, and the breadth of the flat may give 

 us an indication of the period of time for which it has 

 so remained ; such a terrace, however, may be com- 

 pletely obliterated by the tropical rainfall. The ab- 

 sence of a terrace and of loose masses of rock off a steep 

 glacis or slope may well arouse in us suspicions of the 

 existence of subsidence, and we shall be tempted at 

 low tide to row round, to observe whether signs of 

 aerial weathering are visible on the submerged parts 

 of the rocks, and perchance to carry out a few sound- 

 ings. Pillars, etc., of any permanency, such as exist 

 in the Bay of Naples, are unlikely to have been erected 

 by the shore on any land we visit, and it is only by 

 exact survey and careful study of the topography of 

 the slope that we can arrive at any conclusions on the 

 matter. A rugged coast, deep bays or fiords, a fairly 

 constant slope without steeps to a few hundred 

 fathoms or so, might indicate subsidence ; but such 

 observations belong rather to the Hydrographical 

 Offices of the Admiralties — they are scarcely within 

 the compass or time of the visiting naturalist. A close 

 line of soundings out from the shore (made, if neces- 



