212 PHYSIOGRAPHY. [chap. 



though they are now found several feet above high-Yi^ater 

 mark. 



Evidence of the depression of land in Britain is just as 

 conclusive as that of elevation. It is sometimes possible to 

 see, at low tide, in the estuary of the Thames, the remains 

 of a vast forest, with the stools or stumps of the trees still 

 rooted in the old soil, now submerged to a depth of perhaps 

 twenty or thirty feet below high-water. The relics of this 

 ancient forest show that it must have supported a rich growth 

 of yew, pine, oak, alder, and other trees. Now, as these trees 

 do not grow in water, it is evident that the land on which 

 they flourished has been depressed. In some places, the 

 remains of the old land-surface have been buried, to a depth 

 of several feet, beneath alluvial deposits which have been 

 thrown down by the river. When the marshy land on the 

 coasts of Kent and Essex, bounding the estuary of the 

 Thames, is cut through, the sections frequently expose the 

 ancient peaty soil, rich in vegetable remains. This was the 

 case, for example, during the progress of the Main Drainage 

 Works, when deep trenches were cut through the marshes 

 below Woolwich. It is not, however, only at the mouth of 

 the Thames that such evidence of subsidence is to be 

 found ; for similar submerged forests may be seen at low 

 water at many points of the British coast, especially in 

 Devonshire, Cornwall, and Wales. 



Raised beaches and submarine forests afford as good 

 evidence of the rise and fall of the land as any to be got 

 from the Temple of Serapis. But they are not the only 

 evidence which the geologist can cite, to prove that the 

 surface of the British Isles has suffered frequent changes ot 

 level. Nor are they by any means the strongest. Indeed 

 their vahie lies chiefly in the fact that the movements which 

 they register are of comparatively recent date. That there 



