312 SUBMAEINE FOEEST-BED. 



these submerged forest-beds are comparatively modern deposits, 

 and we can only give them a geological date, mainly by the 

 aid of the evidence derived from the excavations made in our 

 valleys to procure the stream tin. 



There is a good evidence to show that these valleys have 

 been completely swept out by a violent and overwhelming flood 

 of water from the north, and that the grains of tin have been 

 deposited on the bare rock and into its pockets and joints, 

 forming with some of the heaviest portions of the gravel in its 

 upper part a stratum from one to five feet deep. This tin bed is 

 invariably covered by a vegetable deposit, similar to that of the 

 submerged forest-bed, especially in respect of the presence of hazel 

 nuts, which abound both in the forest-bed and in the vegetable 

 stratum which uniformly lies on the tin bearing bed, above 

 which the ordinary river deposits alone are found, the whole 

 having a depth of from 50 to 60 feet in the Carnon and Pentewan 

 valleys. Animal remains and some 3 or 4 human skulls have 

 been found at various depths in these upper beds, some of the 

 skulls being within a few feet of the top of the tin ground. 



We are forced therefore to the conclusion that the geological 

 age of these submerged forest-beds was after and closely 

 following the deposition of the stream tin, since which the coast 

 line has sunk from 20 to 40 feet. 



