BRITISH POSTGLACIAL &> RECENT DEPOSITS. 441 



Mr. W. A. E. Ussher also, in his admirable and exhaustive 

 summary of the evidence, 1 seems inclined to connect the sub- 

 merged forests generally with the stratum of vegetable matter, 

 or of detritus mixed with vegetable matter, which rests directly 

 on the tin-gravels. Mr. Ussher speaks with a full knowledge of 

 the subject, and I do not willingly call in question the reason- 

 ableness of his conclusion ; but, after subjecting all the pub- 

 lished evidence to careful scrutiny, I have been unable to dis- 

 cover the grounds upon which it is assumed that the lower peat 

 and trees which rest upon the tin-gravels are necessarily syn- 

 chronous with the submerged forests exposed upon the present 

 foreshore. In some cases this may be the fact, but it is hard to 

 believe, on the evidence produced, that this correlation can be 

 generally sustained. Take, for example, the section of Happy 

 Union Works, Pentuan. In this section I should suppose that 

 the trees and other remains in bed No. 2 rather than those in 

 bed No. 8 were contemporaneous with the submerged peat and 

 trees which are so often exposed upon the shore at low-water. 

 The latter do not rest directly upon stanniferous gravels. In 

 nearly every case where the nature of the stratum below the 

 forest-bed of the foreshore has been observed this is stated to be 

 clay, and in the reclaimed marsh-land between Marazion and 

 Ludgvan, where the peat sometimes attains a thickness of 4 to 

 7 feet, it is said to rest on a bed containing Carclium edule. In 

 the case of the submerged forest of Mount's Bay the pavement 

 is either clay- slate or bluish sand, and in one place a mass of 

 gravel. It seems to me, therefore, most probable that all the 

 submerged forests and peat which are seen exposed between low 

 and high water, or which occur at or near the present sea-level, 

 rest either upon the older rocks of the district or upon those 

 fluviatile, estuarine, and marine beds or their equivalents, under- 

 neath which the tin-gravels lie buried, sometimes at a depth of 

 60 or 70 feet ; and that the ancient buried forest and peat, 

 which repose directly upon those gravels, are the relic of a much 



1 Geological Magazine, Dec. ii. vol. vi. p. 251 ; The Post- Tertiary Geology of 

 Cornwall, p. 45. 



