64 MR SMITH ON THE CHANGES 



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

 rated, to which it could be attributed, nor, indeed, could 

 any action of a river be imagined capable of producing 

 those effects on surfaces so irregular. 1 '' He supposes they 

 may have resulted from the tedious operation of the atmo- 

 sphere, but the actual change of level affords an easy solu- 

 tion of the difficulty, and in each of the cases cited, we have 

 the additional evidence of such an origin from marine re- 

 mains, 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, gravel, or clay ; but the case is doubt- 

 ful as to those at higher elevations ; 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 not observe any such 



* Since writing the above, I have read with much pleasure Mr Trim- 

 mer's paper on the diluvial drift in Wales and Ireland in the Journal 

 of the Dublin Geological Society. I agree with him entirely as to the 

 well-marked difference between diluvial deposits and those caused by 

 permanent submergence ; and if I differ with him as to the origin of 

 the gravels of Howth and Bray, it does not in the slightest degree af- 

 fect the argument. He appears, 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, remarks, 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 



