580 Geological Society, 



tains its character unaltered. Tlie surrounding district is now ste- 

 rile, and no oaks of equal size exist within many miles of Knighton 

 Bottom, the neighbouring plantations being of very recent origin. 

 Traces of fire and of the axe are said to have been noticed in the 

 bog-wood. Ten feet of peat have been excavated, but the depth of 

 the deposit is not known. The peasantry have a tradition, that the 

 forest was burned down during the reign of Stephen, though Mr. 

 Clarke conceives that its destruction was effected during the occu- 

 pation of England by the Romans. At the head of Bourne Bottom 

 there is also a peat bog, but it incloses only fir trees. The subma- 

 rine peat and forest off the entrance of Bourne Mouth* contains 

 fir, birch, and alder trees ; Mr. Clarke however considers that the 

 two latter have been transported from the bog at the top of Knigh- 

 ton Bottom. Some of the trees, as noticed by Mr. Lyell, are py- 

 ritous, but the author of the paper is of opinion^ that they have been 

 derived from the neighbouring cliffs of plastic sand, having observed 

 in them, during the summer of 1837, a pyritous trunk. The present 

 position of the forest, Mr. Clarke thinks is due to a subsidence and 

 undermining of the strata, which supported it at a higher level. 



Other peat bogs are described on the north of Poole harbour, as 

 between Sterte and Stanley green, at Hatch Pond, Creekmoor and 

 Lytchett. At the first of these localities, in mailing an excavation 

 to erect a dyke, the workmen found beneath the alluvial soil, gra- 

 vel, then peat, and afterwards oaks and alders which rested upon 

 mottled clay. The sea, at all states of the tides, overflowed this inlet 

 previously to the erection of the dyke ; and the position of the forest 

 Mr. Clarke assigns to an undermining of the strata on which it 

 rested. 



At Hatch Pond, about two miles north of Poole, in the direction of 

 Winboum, is an extensive depression through which a brook of 

 some volume flows, and has produced an immense accumulation of 

 peat. This bog communicates with Poole Harbour by a succession 

 of marshy grounds ; the whole of which Mr. Clarke conceives were 

 once covered by the sea, as they present phenomena similar to 

 those exhibited at Tottenham, with the exception that no trees have 

 been observed. A branch of a Roman road meets the present high- 

 way just upon the edge of the depressed area, and the author infers 

 that that point was, in the time of the Romans, the water head of 

 the bay, though it is now three or four furlongs Nearer Poole. 



Creekmoor. Another tract of low marshy ground, with a peat-bog 



* An account of this submarine fir-wood was first given by Mr. Lyell in 

 the 4th edition of the Principles of Geology (1835), from information com- 

 municated by Mr. Charles Harris. The present submerged position was ex- 

 plained on the belief, that as the sea is encroaching on the shore, the Bourne 

 Valley may once have extended further; and that its extremity consisted as 

 at present of boggy ground, partly clothed with fir-trees; that the sea laid 

 bare at low tide the sandy foundations, which being undermined by streams 

 of freshwater, several of which burst forth in different parts of the existing 

 beach, the matted superstratum of vegetable matter sank down below the 

 levjl of the sea.— Vol. iii. p. 276. 



