OF THE SEA AND LAND. 21 



the diminishing resistance of man. As Alexandria and 

 Carthage have been replaced by Amsterdam and Peters- 

 burgh, so will these give away to new cities in other 

 lands, when the term of their prosperity shall be com- 

 pleted. From the same causes islands become penin- 

 sulas; and, of this, Gibraltar is a conspicuous instance : 

 as are in our own country, the Mull of Cantyre, and 

 the Garroch head of Bute, with the promontories of 

 Hillsvvick and Surnburgh head in Shetland. Such 

 changes are in themselves subject to change : from 

 variations in the level or currents of the sea, arising from 

 analogous or other causes ; and thus have such tracts 

 been found to vacillate from the one to the other cha- 

 racter. 



Of the variations in the outline of the sea, few are 

 more important than those by which bays and deep 

 inlets are filled, and converted into land. This occurs, 

 independently of the deposits of ^reat rivers, by a con- 

 currence of the movements of the tides with the forms 

 and directions of shores : the moveable alluvia of the sea 

 being deposited to the lee of the currents, where, aided 

 occasionally by the ruins of the land, and by submarine 

 vegetation, they form banks which first shoal and de- 

 stroy the harbours, and lastly convert them into plains. 

 In many of the deep inlets of the Highlands, as in Loch 

 Tarbet, this process is very sensible : as, in the other 

 case, the bay s on each side of the Chesil bank are gradually 

 diminishing in depth ; the finer materials subsiding, to 

 the eastward, under shelter of that ridge, while to the 

 windward, the same bank, checking the direct motion 

 of the gravel, accumulates what the western swell rolls 

 on. But the different modes in which these effects are 

 produced, vary in almost every place ; and among them, 

 few are more remarkable than those which occur in the 

 islands of the Indian ocean ; where the growth of ma- 



