484 Correspondence — Mr. A, B. Wynne, 



from a long series of observations, that, in common with other slope 

 drifts in England and Wales, the bulk of it is not a mere disintegra- 

 tion in situ, but the effect of lateral displacement in a great measure 

 irrespectively of the form of the ground. D. Mackintosh. 



liniKENHEAD, 12th Sept., 1868. 



OX THE DISTURBANCE OF THE LEVEL OF THE LAND NEAR 

 YOUGHAL, ON THE SOUTH-EAST OF IRELAND. 



Sir, — In your May number, which has just reached me, I find 

 Colonel Greenwood considers me in " error" when supposing de- 

 pression of the land necessary to account for facts observed at 

 Youghal ; but in the remarks which follow this I fail to see that the 

 author of '' Eain and Elvers," while admitting one of my proposi- 

 tions, proves the other wrong. 



If it be granted that as the sea erodes a line of coast at rest the 

 beach may travel landward, surely while the sea erodes " the whole 

 line of coast," the peat beneath the travelling beach ought to be 

 eroded also, and disi^ersed instead of being submerged. The peat 

 under Youghal Bay, however, not having been eroded and dispersed, 

 we may conclude that the land there was not at rest during the sub- 

 mergence of the peat. 



But the gist of Colonel Greenwood's argument lies in his assertion 

 that " the stream or the rain valley cuts its estuary far deeper [how 

 much ?] even than low- water-mark," forming an arm of the sea. 



Applied to the case in point, that is to say, that the rain valley ex- 

 cavated its estuary as much lower than sea level as is the surface 

 upon which the first peat was formed, now far out under Youghal Bay. 

 This point must be at a considerable depth, if my memory and infor- 

 mation be correct, for I have seen from three to five fathoms water 

 marked upon a chart somewhere about the place indicated by fisher- 

 men as the outer limit of where peat is known to occur. To this 

 depth must be added the unknown thickness of the peat, which in 

 parts of Ireland not uncommonly exceeds 20ft. However, taking it 

 at 10ft., we have thus a rain-and-river valley excavated by these 

 agencies to a depth of from 28ft. to 38ft., or, it may be, 40ft. or 50ft., 

 below the level of the sea at low water ! 



Depression not being admitted, is it not fair to ask whether the 

 beach of that period may have been of this height, and what kept 

 the sea out of the valley before the beach Avas thrown up by some 

 storm, so that peat could grow behind it? I may also, I trust, be 

 excused for asking, if the stratified sand, gravel, and clay, with flints, 

 which forms Clay Castle Hill, was thrown up to a greater height 

 than 91ft. by storm, or ordinary waves, or otherwise, how does it 

 come to contain sea shells at such a considerable elevation as it does ? 



I must here confess that " raised beach'' is not an expressive term 

 for such a local accumulation as that of Clay Castle, and was only 

 used for want of a better. All low ground gradually elevated from 

 the sea would, at one time or another, have formed its beach (as was 

 once remarked to me by Professor Jukes), therefore one locality has 

 no better claim than another to the name, used in a general sense. 



I 



