§24. LEWES LEVELS. 61 



direction of the currents. Frequently, too, worms and 

 molluscous animals crawl over and mark the surface with 

 meandering lines, and ridges ; and these varied characters 

 on the sand are preserved, if a thin layer of mud happens 

 to be deposited over them before the next advance of the 

 waves. I shall have occasion to refer to these appearances 

 hereafter. We may also remark that certain kinds of 

 mollusca, or shell-fish, can only live in fresh water ; others 

 are confined to the sea ; while a third class is restricted to 

 the brackish waters of estuaries ; accordingly, in the de- 

 posits under consideration, the river and estuary species are 

 abundant, while the marine only occur as stragglers, and 

 are comparatively rare. Land plants, and those which 

 affect a marshy soil, as the equiseta, or mare's-tails, reeds, 

 rushes, &c. are likewise often accumulated in such quantities 

 as to form beds of peat. 



24. Lewes Levels. — It will serve to impress the sub- 

 ject more forcibly upon our minds, if we refer to some 

 local example of fluvio-marine deposits: and from its imme- 

 diate vicinity to Brighton, I select that which occurs in the 

 valley of the Ouse, near Lewes, which is one of several 

 estuaries whence the sea has retired within the last eight or 

 ten centuries. This tract is about eight miles in length 

 from north to south, and varies in breadth from half a mile 

 to two miles and a half. The valley is bounded by an 

 amphitheatre of chalk hills, into which the river enters 

 through a gorge of the Downs on the north, near Offham, 

 and pursuing a tortuous course, flows between the towns of 

 Lewes and The-Cliff, and discharges its waters into the sea 

 at Kewhaven. This alluvial plain is called Lewes Levels, 

 and is here and there flanked on the east and west by head- 

 lands, and ancient sea-cliffs; while a few insular mounds of 

 chalk rise up through the fluviatile deposits, that have been 

 accumulating during a long period of time. Lign. 7, repre- 

 sents a section of the valley of the Ouse, from east to west. 



