The Scalp, County Dublin. 243 



accumulations elsewhere ; and if this is correct, the Carboni- 

 ferous hills of the Dublin plain must have disappeared 

 thousands and thousands of years before the Scalp existed. 



But had the denudants anything to do with the Scalp ? 

 To me it would seem that they had not. Ireland was under 

 water or ice, or some such envelope, and when " the dry land 

 appeared," it contracted during the drying process, and 

 shrinkage-fissures formed. This subject has been very ex- 

 hausti^'el}^ entered into in my work on "Valle3^s and their 

 relation to Faults, Fissures, etc.'" and especially in chapter ii. 



In 1878, I suggested in the ''Geology of Ireland" that the 

 Scalp was " probably excavated by marine action aided by ice 

 along dykes of fault-rock." Since then, however, I have had 

 opportunities of more carefully stud3dng it and similar valleys, 

 and would be inclined to suggest that it is nearly solely due to 

 simple shrinkage-fissures, and that, since its formation, it has 

 not been subjected to the effects of any denudants. 



A study of the ravines, the adjuncts of the granite range of 

 Leinster, shows that these are of different ages, some being 

 comparatively recent. The ravine of the I^iffe}^ at Poulaphuca 

 must be very modern, as the river-bed in which it formerly 

 flowed southward is still very conspicuous and unchanged. 

 The valley of the Slaney must have opened before or during 

 the Esker sea period, as in it is found the marine drift. The 

 valley of Tinnahely is probably older, as it is in parts occupied 

 by moraine detritus ; while the Devil's Glen, like the Scalp, is 

 due to a movement that took place at quite a recent date. It 

 may be allowable to suggest that the ravines at Poulaphuca, 

 the Devil's Glen, and the Scalp, were formed at about one and 

 the same time ; that is, after the ice-cap had disappeared, and 

 the Esker sea had retreated, so that now, in none of these, is 

 there found drift of any kind, except meteoric accumulations, 

 still daily forming." 



Waterford suggest estuarine accumulations ; at the same time it must be 

 allowed that these small areas may be the remains or roots of the formed 

 Carboniferous sheet. Low down in the Queen's Co. and Tipperary fields 

 there is a continuous massive sandstone made up almost solely of granite 

 detritus. 



* Triibner and Co., London, 1875. 



- In the Scalp there are said to be foreign blocks ; these, however, may 

 have come down from the drift. 



