Correspondence — 0. H. Kinahan. 189 



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MR. BIRDS ON THE IRISH GLACIAL DRIFTS. 



Sir, — In a paper in the Geological Magazine for Feburary, " On 

 the Post-Pliocene Formations of the Isle of Man," the author, Mr. J. 

 A. Birds, intimates that an Upper Glacial Drift with underlying 

 " Middle Gravels " has been proved to exist in the east of Ireland. 

 If, however, this observer had read all the evidence on the subject, 

 he would know that if such divisions exist, they have never yet been 

 found. 1 If such drifts exist, they ought to be found in some of 

 the cuttings for the numerous lines of railway that traverse 

 Ireland ; but as yet no section showing them has been exposed. 

 In the east of the Island they might be expected to be found, 

 in the cuttings for the railways between Dublin, Belfast and 

 Larne, or Belfast and Newcastle, or Dublin and Wexford ; yet they 

 have not been exposed ; and if they did exist, they could scarcely 

 have been passed over in the cuttings between Drogheda and 

 Belfast. In the Dublin and Wexford railway, north of Killiney 

 hill, and both N. and S. of Bray Head, there are indeed Boulder- 

 clays, that a casual observer might suspect to be normal Glacial Drift; 

 but a very slight examination ought to satisfy him that these sus- 

 pected Upper Glacial Drifts were members of the Gravel Drifts ; 

 having been either talus, due to the weathering of a Glacial Drift cliff, 

 or slips from the latter, that had covered sands and gravels, which 

 had accumulated at the base of the cliff. In the east of Ireland 

 the only place where there seems to be drifts at all likely to be 

 Upper Glacial Drift and Middle Gravels, is at the Mourne mountains, 

 on the west coast of Dundrum Bay, and in the Mourne Demesne ; but 

 in both places a very brief examination will show that the upper 

 member of the sections cannot be normal Glacial Drift. The writer 

 of the paper to which I allude has evidently fallen into the mistake 

 made by so many writers of the present day on Drift, — that is, of in- 

 cluding in Glacial Drift all Boulder-clays, if glacialoid, and also the 

 associated gravels and the like ; while it is evident that. all stratified 

 Boulder-clays cannot be normal Glacial Drift ; for since the materials 

 were imbedded in ice, they must have been re-arranged by water ; 

 while many unstratified Boulder-clays cannot be normal Glacial 

 Drift, as their present position is due to the slipping or weathering 

 of cliffs. All gravels, sands and the like, cannot possibly be called 

 Glacial Drift, as they have been not only re-arrangecl, but also sorted, 

 sifted, and transported, since they came out of the ice. 



If the age of the Glacial Drift is allowed to be proved by such loose 

 evidence as that which is now so commonly in vogue, proofs mio-ht 

 be adduced that it is in course of formation, even up to the present mo- 

 ment. In numerous places cliffs of Glacial Drift exist, at the base 

 of which sands, gravels, alluvium, and peat are accumulating, or 

 human works are being constructed. These cliffs in time must form 

 slopes, either by weathering or slipping : and thereby cover up what 



1 See Middle Gravels (?), Ireland, Geol. Mag., 1872, Vol. IX. p. 265, and Glacialoid 

 or Re-arranged Glacial Drift, Geol. Mag., March and April, 1874. 



