288 ALLUVIUM. 



an extensive basin of salt water, into a fresh water lake*, and of the 

 transition of the latter into a narrow river, which now flows through a 

 fertile tract formed of the detritus of other strata, brought in remote 

 ages from the interior of the country, and deposited in a valley of the 

 chalk formation. 



2. Subterranean Forests. 



The occurrence of large trees beneath the surface of the earth, with 

 their leaves, roots, and even fruits, more or less preserved, attracted the 

 attention of philosophers at a very early period. . These subterranean 

 forests have been noticed in almost every part of England, and various 

 conjectures offered in explanation of the catastrophes by which they have 

 been overwhelmed. The subject has been ably treated by Mr. Parkin- 

 son f, to whose work the reader is referred for an interesting account of 

 the most remarkable examples. 



The trees are chiefly oak, hazel, fir, birch, yew, wiUow, and ash ; in 

 short, almost every kind that is indigenous to this island occasionally 

 occurs. The trunks, branches, &c., are dyed throughout of a deep ebony 

 colour; the wood is firm and heavy, and sometimes sufiiciently sound 

 for domestic use ; in Yorkshire it is employed in the construction of 

 houses. Several accumulations of this kind have been discovered on the 

 coast of Sussex, occupying low alluvial tracts, that are still subject to 

 periodical inundations. 



At Felpham, near Bognor, on the 25th of October, 1799, a submarine 

 forest was laid bare by a north-east hurricane. It was situated about five 

 feet beneath the surface ; but neither its thickness nor extent could be 

 ascertained ; notwithstanding, there can be no doubt, that it pervades the 



* This conclusion naturally results from the occurrence of marine shells in the lower beds 

 only, and of fresh water in the upper, the two being intermixed in the intermediate layers; 

 since the experiments of M. Beaudant have shewn, that if fresh water moUusca be suddenly 

 introduced into sea water, they die in a vei'y short time ; but if the fresh water is very gradually 

 impregnated with salt, they will live in it when of the strength of sea water without any injury: 

 the same experiments repeated on fresh water mollusca gave similar results. Vide Annal. de 

 Chim, et Physique, ii. 32. 



f Organic Remains, Vol. i. p. 62, et seq. 



