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Ch. XLVIII.] 



IN SUBAQUEOUS STRATA. 



569 



enclosing shells of existing species * Tlie Chara also plays 

 the same part in the subaqueous vegetation of North 

 America as in Europe. I observed along the borders of 

 several freshwater lakes in the state of New York a luxuriant 

 crop of this plant in clear water of moderate depth, rendering 

 the bottom as verdant as a grassy meadow. Here, therefore, 

 we may expect some of the tough seed-vessels to be preserved 

 in mud, just as we detect them fossil in the Eocene strata of 

 Hampshire, or in the neighbourhood of Paris, and many 

 other countries. 



IMBEDDING OF FRESHWATER SPECIES IN ESTUARY AND 



MARINE DEPOSITS. 



In Lewes levels. — We have sometimes an opportunity of 

 examining the deposits which within the historical period 

 have silted up some of our estuaries ; and excavations made 

 for wells and other purposes, where the sea has been finally 

 excluded, enable us to observe the state of the organic remains 



The valley of the Ouse between Newhaven 

 and Lewes is one of several estuaries from which the sea 

 has retired within the last seven or eight centuries; and 



in these tracts. 



om the researches of Dr. Mantell, 

 rrls in thickness have accumulated 



At 



the top, beneath the vegetable soil, is a bed of peat about 



many 



Next 



stratum 



nine species, such as now inhabit the district. Intermixed 

 with these was observed the skeleton of a deer. Lower down, 

 the layers of blue clay contain, with the above-mentioned 

 freshwater shells, several marine species well known on 

 our coast. In the lowest beds, often at the depth of 36 feet, 

 these marine Testacea occur without the slightest inter- 

 mixture of fluviatile species, and amongst them the skull of 

 a narwal, or sea-unicorn {Monodon monoceros) , has been de- 

 tected. Underneath all these deposits is a bed of pipe-clay, 

 derived from the subjacent chalk.f 



^ Dr. Bigsby, Journ. of Science, &c,, also Catalogue of Org. Kem., Gaol. 



No. xxxvii. pp. 262, 263. 



t Mantell, GeoL of Sussex, p. 285 ; 



Trans, vol. iii. part i. p. 201, 2nd series 



