26 



regard to area and fish- rearing capability ; the remainder 

 are either so small or suffer from such disabilities as to 

 be of minor importance. 



The various sections are bounded and divided from 

 each other partly by natural divisions consisting of 

 natural tongues of land and chains of islands and sand 

 banks, and for the rest by artificial earthwork dykes 

 connecting the islands and miniature peninsulas into 

 continuous embankments. Where necessary the foot of 

 the dyke on one or both sides is strengthened with rows 

 of stakes. The earthwork itself is the sandy mud from 

 the bottom of the lagoon ; there is generally a large ad- 

 mixture of broken shells in it and this is considered to 

 have a beneficial effect in the consolidation of the 

 rampart. The sedges and grasses which grow freely 

 over the slopes are further useful factors in the work of 

 consolidation. 



The sand-bank peninsulas and chains of islands 

 nearly all run in a direction north and south, roughly 

 parallel with the present sea-coast. The best defined 

 chain divides the lagoon into two almost equal parts. 

 The western or inner half is again subdivided by a dyke 

 into two distinct and very large fish-rearing valli, the 

 Mezzano of 17,407 hectares and that of Fossadiporto of 

 2,701 hectares. The eastern or seaward half of the 

 lagoon contains the remainder of the fish-farms, very 

 numerous, very irregular in outline and often compara- 

 tively small. The depth of water in the valli is never 

 great, it ranges generally between 3 and 6 feet but in 

 times of drought large sections of the bottom become 

 drv through the shrinkage of the water area. 



All the valli are in more or less direct communication 

 with the sea by means of canals opening from one of 

 two sea-mouths traversing the Lido, that natural break- 

 water which protects the lagoon from the inroads of the 

 sea. The principal sea-mouth, that called the Port of 

 Magnavacca, cuts through the Lido almost midway be- 

 tween the embouchure of the Volano and the Reno. Its 

 length is about 2 kilometres, by 40 metres (131 "2 feet) 

 wide, and 2J metres (8*2 feet) deep at mid-tide. The 

 banks are heavily timbered and two wooden groynes 

 or breakwaters defend the seaward end. This mouth 

 feeds the whole of the fish-farms with sea-water, with 



