I 



On Lines of Ancient Sea-Levels. 125 



having been raised to mneli greater heights than others. Tlie 

 examination of the mountains of North Wales and the adja- 

 cent plains of Shropshire, for example, could lead to no other 

 inference ; there being in tracts absolutely contiguous, a dif- 

 ference of not less than 1000 feet between the level at which 

 the same species of marine shells are now lying ; and as no 

 other portion of England or South Wales offers a trace of tes- 

 tacea at the higher of these altitudes, it is demonstrable, that 

 when the sea deposited the shells in Moel Tryfane it did not 

 stand at that height above the whole of England, but that the 

 local appearances resulted simply from unequal elevation of 

 the sea'*s bottom. 



All the analogous phenomena in the British Isles seem to 

 lead to the same conclusion. Whilst the modern marine al- 

 luvia of the central counties are found to rise towards Snow- 

 don as a great centre of elevation, the banks of gravel with 

 similar shells ascend from the coasts of Lancashire towards 

 the Penine chain in the interior. Again, in the south-west of 

 England, the most distinct sea-beaches yet noticed, w^ere as- 

 certained to rise very perceptibly from a low level on the south 

 coast of Devon and Cornwall, to heights of 120 feet above tlie 

 sea in North Devon, where the elevation is more intense. The 

 valley of the Severn afforded similar proofs ; the beds of gra- 

 vel with sea-shells, between Worcester and Gloucester, near 

 its estuary, are slightly elevated above the sea ; but in ascend- 

 ing to its source, the same gravel and shells occur at altitudes 

 of 500 to 600 feet, until finally they are seen in the lofty cliffs 

 of Moel Tryfane, before alluded to. 



Whilst such may be justly received as absolute proofs (quite 

 as clear as those of M. Bravais) of more intense elevation at 

 some points than at others, the submarine forests along our 

 coasts have been supposed to offer proofs of subsidence. These 

 evidences, however, are not of the same satisfactory nature as 

 those of elevation, for it may in some instances be contended, 

 that the forests in question grew upon low deltas, and have 

 been overwhelmed by irrnptions of the sea, which broke down 

 certain banks or natural barriers, that at one period protected 

 them from inundation. But granting these submarine forests on 

 the east coast of England to be really as good proofs of a de- 



