390 Mr Smith on the Changes of the Level of the Sea. 



once have existed at least at the same level as the summits of 

 the present dykes. Nor can any obvious causes now be traced 

 by the operation of which so great a removal of land has been 

 effected ; there are no rivers in any of the instances enumera- 

 ted, to which it could be attributed, nor, indeed, could any ac- 

 tion of a river be imagined capable of producing those effects 

 on surfaces so irregular." He supposes they may have result- 

 ed from the tedious operation of the atmosphere, but the actual 

 change of level affords an easy solution of the difficulty, and in 

 each of the cases cited, we have the additional evidence of such 

 an origin from marine remains, embedded in the alluvial strata 

 which accompany them. 



Although we have traces of changes of level on every side of 

 the British Islands, it would be premature to say whether or 

 not they are all universal, or whether some of them may not be 

 confined to particular districts. There can, I apprehend, be 

 no doubt as to the lower levels under the great terrace ; the 

 plateau at its base, except where since worn away by the action 

 of the sea, is invariably composed of marine beds of sand, gra- 

 vel, or clay ; but the case is doubtful as to those at higher ele- 

 vations ; and if the shells at the top of the mountain of Moel 

 Tryfane be considered as a proof of elevation, we may safely 

 assume that it must have been a local one. * Although we do 



* Since writing the above, I have read with much pleasure Mr Trimmer's 

 paper on the diluvial drift in Wales and Ireland in the Journal of the Dub- 

 lin Geological Society. I agree with him entirely as to the well-marked 

 difference between diluvial deposits and those caused by permanent sub- 

 mergence ; and if I differ with him as to the origin of the gravels of Howtk 

 and Bray, it does not in the slightest degree affect the argument. He ap- 

 pears, for he has not come to that part of the subject, to consider them the 

 result of diluvial action, whilst I agree with my friend Dr Scouler, with 

 whom I visited them, that they are proofs of elevation. Mr Trimmer, 

 after noticing the ready reception of the diluvial theory of Buckland, re- 

 marks, that " the interest excited by these new and striking facts {i. e. proofs 

 of change of level) had now diverted the current of geological speculation 

 into an opposite direction from that in which it had lately flowed, and from 

 the one extreme of having generalized too hastily on diluvial phenomena, 

 geologists began to run into the other, of endeavouring to exclude diluvial 

 action from the list of geological agencies, — to expunge the very name from 

 geological nomenclature, — to forget all the evidence which had been col- 

 lected of the passage of large bodies of water over the land, and, in every 

 mass of transported gravel in which marine shells of existing species were 



