W. A. E. Ussher — Pleistocene Geology of Cornwall. 251 



V. — Pleistocence Geology of Cornwall. 1 



By "W. A. E. Ussher, F.G.S. 



Part IV. — Submerged Forests and Stream Tin Gravels. 



THE evidence under this head is necessarily a compilation; the 

 very exceptional exposure of the old forest ground, and the 

 nature of stream tin sections, leaving no room for personal investi- 

 gation. The names of the observers are in most cases sufficient 

 vouchers for the accuracy of their statements. The submerged 

 forests are given first, as there is no evidence forthcoming to show 

 the priority of the stream tin gravels to the general growth of the 

 forests. The forest bed overlying the stream tin which Mr. Carne 

 rightly synchronizes with the forest beds on the coast may represent 

 a very brief portion of a long period of forestial growth. 



Submerged Forests. — Proceeding round the coasts from Plymouth. 



1. Looe. Mr. Box (26th Ann. Eep. Eoyal Inst. Corn, for 1844) 

 noticed trunks of oak, alder, ash, and elm, on Millendreath Beach, 

 in vegetable mould extending for 250 yards from east to west, and 

 sloping from below high-water mark to the southward for 150 feet, 

 where it was lost sight of under fine sand, which, though explored 

 for 30 feet farther out, yielded no further traces. The plants in the 

 mould resembled those found in a neighbouring marsh, 130 feet 

 above high water, of which the following section is given : — 



Peat of flags and arundaceous plants. 



Dark brown vegetable matter witb bolly and alder. 



Layer of sand witb vegetable matter, numerous bazel nuts, and tbe elytra 

 of Coleopterous insects, also black oak and ? bolly, resting on firm light- 

 coloured clay. 



Numerous angular slate fragments were met with, but no shells. 



2. Near Mevagissey. Sir G. Lemon (T. E. G. S. Corn. vol. vii. p. 

 29) gives the following section disclosed in cutting a drain at Heli- 

 gan (about a mile inland from Mevagissey Bay) near the foot of a 

 hill 20 feet above the stream in the valley bottom, and in another 

 place, higher up, at 40 feet above the stream : — Loam 1 foot 8 inches 

 from the surface, upon a mass of whitish, bluish, and yellowish clay 

 with broken slate, with the stump of an oak 4 feet long and nearly 

 a foot in diameter, 7 feet 4 inches from the surface at its lower 

 extremity. 



Submerged forests have been observed after severe gales — 



3. At Fowey by Mr. Peach (T. E. G. S. Corn. vol. vii. p. 62), the 

 trees being rooted in stiff clay. 



4. At Porthmellin, near Mevagissey (Ibid, vol. vi. pp. 23 and 51), 

 the roots resting on clay apparently in situ. 



5. At Maen Porth, near Falmouth, by the Eev. J. Eogers (Ibid, 

 vol. iv. p. 481), the roots being in clay. 



6. At Porthleven near the Loo Pool, by the Eev. J. Eogers (Ibid, 

 vol. i. p. 236), oak and willow roots apparently in situ. At Fowey 

 and Porthmellin, elytra of beetles were found. 



7. Mr. H. M. Whitley (Journ. E. Inst. Corn. No. 13, p. 77) gives 



1 Continued from tbe May Number, p. 211. 



