8 Wynne — Denudation and its Causes. 



to the action of recent marine erosion, unless it be admitted that the 

 seas at full tide can cut high cliffs out of hard rocks, and carry away 

 their debris without removing the soft peat which rests near their 

 base. 



The part of the Irish Coast reaching from Waterford westward by 

 Mine Head to beyond Youghal Bay presents from the sea a line of 

 cliffs, with some intervals, where valleys open upon it. At the latter 

 place a quantity of peat may be observed between tides along the 

 strand ; approaching at one spot within a few yards of the cliffs at 

 the mouth of the Eiver Black-water.^ 



If the coast line here merely coincides with a portion of an older 

 one we should expect to find the old sea cliff following inland such 

 contour lines of the ground as would include the present one, but 

 although the ridges of that country frequently have steep sides, there is 

 no inland cliff continuous with that which edges the coast, nor is there 

 any reason to believe in the existence of one concealed by drift. Sup- 

 posing the coast line now to coincide entirely with an earlier one, the 

 land since the latter was produced must have presented a marked range 

 of cliffs, at some unknown distance from the sea, such as is not now 

 to be found at a greater altitude* in that neighbourhood, and must 

 subsequently have been depressed almost exactly to the same level 

 which it occupied before the peat was formed, and this without the 

 peat having been washed away during the depression or since it 

 occurred. 



Otherwise, if we suppose the denudation of the valleys which open 

 upon this coast to have removed continuations of the older cliffs, 

 either inland or across their mouths, while the formation of the now 

 submarine peat was taking place it follows that this denudation was 

 subaerial and unconnected with the sea, thus pointing to the 

 probability that the outlines of coasts are mainly the results of 

 depression, and that their configuration frequently depends upon 

 forms produced by subeerial denudation.'* 



^ The Valley of whicli is attributed to subserial denudation by Professor Jukes in 

 his able paper and interesting letter, See Quart. Journ. Geol. Soc. Lond., Vol. xviii., 

 and Geological Magazine, Vol. III., No. 5, p. 232. 



With reference to the foot note to Mr. Kinahans paper. " On the Eock basin of 

 Lough Corrib," Geological Magazine, Vol. III., (Nov. 1866,) p. 495. — Supposing 

 the morass mentioned to be below high water mark, if a sand bar was thro^'^l up by the 

 sea, the swamps behind it would naturally become a receptacle for peat independently 

 of the prior submergence of other localities. The argument requiring the former 

 existence of sand bars around so much of the bolder coasts of Ireland, hardly explains 

 their wholesale removal, while the supposition of depression would agree with the 

 similar occurrence on the East Coast of England. (See Mr. J. Geikie's paper " On 

 the Forests and Peat Mosses of Scotland. Trans. Rl. Soc, Edin., Vol. xxiv). In the 

 example at Youghal a beach has been thrown up above and resting on the peat, which 

 is said to extend out beneath the bay at low water, and was observed when the tide 

 was very far out, or nearly at its lowest, beneath the sea as far as footing could he 

 obtained. 



2 Among many examples showing somewhat of the rate of erosion eifected by the 

 sea, the case of the all but pre-historic Beehive Village of Fahan, in Kerry, may be 

 mentioned — a portion of which remains upon the verge of the sea cliffs at Slea Head: 

 or the tradition that Horse Island has been detached by the sea from Bolus Head in 

 the same county ; similar instances, save in the softer nature of the materials removed, 

 are the old Abbey and graveyard encroached upon by the sea at Ballinskelligs Bay, 



