244 The Irish Naturalist. 



Let us suppose that the Scalp was excavated by a stream 

 flowing south. If so, where is now the granite detritus that 

 was excavated? The nearly total absence of all granite 

 detritus in the drift of the Bray and Bnniskerry valley is re- 

 markable ; in fact, you find nearly as many blocks of con- 

 glomerate (from Portraine and Rush) as of granite. It has 

 been suggested that possibly the numerous pieces of limestone 

 in the drift of the country south of the Scalp range came from 

 the ''Dublin Carboniferous hills" through the Scalp gorge. 

 As, however, this drift in which the limestone is found is 

 glacial, it would necessitate that the drift was carried by ice, 

 not normal water ; but in the Scalp there is not a trace of 

 glacial or any other drifts, except aeolian and meteoric. Com- 

 pare the Scalp with the nearest valley, Glencullen, The latter 

 must be much more ancient, as in it are different phases of 

 the accumulation of drift — first, moraine matter that was sub- 

 sequently denuded by the force that excavated the stream - 

 ravine ; then, still more subsequently, there were modifica- 

 tions due to meteoric abrasion and its adjuncts ; the latter 

 still taking place. In fact, this longitudinal valley must be 

 more ancient than the transverse one. 



In favour of the formation of the Scalp being due to a 

 shrinkage-fissure, the enquirer's attention may be directed to 

 the numerous facts recorded in the book already referred to 

 (" Valleys and their relation to Faults, Fissures etc."). 

 Numerous examples might be given of shrinkage-gorges, 

 but we will only refer to one; as this valley, in its general 

 characters, is very similar to the Scalp. The example to 

 which I refer is Barnesbeg, Co. Donegal, through which the 

 road from Kilmacrenan to the country on the northward has 

 been made. To me it would appear evident that this valley 

 owes its origin to a combination of shrinkage-fissures, one of 

 which at least, as in the Scalp, caused a lateral displacement, 

 but associated with them there is no record of any drift-form- 

 ing agent. The fissures formed, while subsequently atmos- 

 pheric abrasion and disintegration came into force, blocks 

 falling from the different marginal cliffs to form rocky tali, 

 the blocks being slightly modified by meteoric action, while 

 the detritus thus formed was carried away by the winter and 

 summer floods. Thus here, as in connection with the Scalp, 

 there is no accumulation, that can legitimately be called drift. 



