ALLUVIUM. 285 



XX. 



§ IV. 13. ALLUVIUM. 



Under this name are included, 



1. Marsh land, composed of blue clay, silt, &c. produced by rivers. 



2. Peat, and subterranean forests. 



3. Calcareous tufa, deposited by springs. 



4. Sand, and comminuted shells, on the coast, and drifted inland. 

 These depositions are clearly the effect of local causes which still 



continue in operation, and appear to have proceeded with but httle 

 modification, from the period when our continents assumed their present 

 form *. 



In Sussex, the marsh lands (No. 1), which from the flatness of their 

 surface, have received the provincial name of " levels," constitute several 

 extensive tracts, partially filhng up vaUies in the older formations. They 

 perfectly correspond in the nature of their materials, and for the most 

 part have a river flowing through them. A description of those of 

 Lewes will serve to convey a correct idea of the whole. 



Lewes levels, have aheady been noticed as constituting a flat 

 marshy tract, through which the river Ouse winds its way to the British 

 Channel. Tradition, ancient records, and the names of several hamlets f 



* Phillips' Geology, (Edit. 1822), p. 4. f Hamsey, Landport, &c. 



