■30 Proceedings of the Eoyal Irish Academy. 



HaTigliton's definition of the "Head of the tide," is not quite 

 correct. It onglit to be — no surface cn,rrent. It is evident, as the 

 •water comes in, and subsequently goes out below, there must be 

 ■considerable deep-seated currents — as indeed is evidently proved in 

 the estuary of the Mersey, the currents there being adjuncts of the 

 great "Head of the tide" in the neighbourhood of the Isle of Man. 

 On chart jS^o. 45, a considerable "race" is marked round the Bill of 

 the Mull, also in the south portion of the "Beaufort's Dyke." 



It is allowable to speculate as to the reasons why the gulch 

 has in it shifting sands and their adjuncts. It is known that, 

 on account of the rotation of the earth, the rise of the tides on 

 the British side of the channel is greater than on the Irish side ; 

 therefore, at the northern Hinge-line, the denudation, due to the 

 deep-sea currents, ought to be greater on the British side than on the 

 Irish side — this seems to be the case, by the records on the different 

 charts. If this is allowed, there ought to be, at this Hinge-line, the 

 greatest currents, in and out, at high-water of spring tides, in the 

 -vicinity of the eastern coast-line — that is, o-ffi the shore of the Mull of 

 Galloway ; and these tidal currents should, during the ebb of the 

 springs, carry the sands and their adjuncts iu the gulch northward, 

 and, during the flow, southward — each carriage, either northward 

 or southward, being more or less augmented by favourable wind- 

 waves. Thus, if there were continuous winds fi'om tfie southward, 

 the sands, etc., should accumulate towards the north of the gulch — 

 the northward carriage being at a maximum ; while, if there were 

 continuous winds from the northward, to augment the flow tidal 

 currents, the southern portion of the gulch should be more or less 

 filled up. 



These changes in the carrying powers of the currents would 

 fully account for "the Pulls" being sometimes to the southward, 

 and at other times to the northwai'd, in the gulch ; but there is 

 still an anomaly in the deep that, according to the charts, seems 

 always to exist south-west of the Bill of the Mull. This deep some- 

 times is gradually connected with the other deeps in the gulch, but 

 often it is separated from them by an accumulation. How, therefore, 

 is this accumulation to be accounted for ? It may be suggested that, 

 at the turn of the tide, the pent-up water in the " Head of the tide," 

 rushes into the south end of the gulch, and cleans it out. This, 

 however, will not account for the formation of the intercepting ac- 

 cumulations. This, possibly, may be due to the di'iftage southward 

 due to the flow tide, augmented by the wind-waves not being 



