94 The Irish Naturalist. 



When we know that, in Sicily, Pliocene beds are found 3000 

 feet above the sea, and yet 80 per cent of the molluscan species 

 found in them still flourish in the Mediterranean, we need not 

 recoil from seeing in the recent species on the Dublin Moun- 

 tains evidence of earth-movements of one half this magnitude. 

 But another question rises ; might not the shells have been 

 stranded in hollows of the hills during a subsidence prior to 

 the cold period ? Elevation then followed ; and, the hills being 

 brought above the snow-line, glacial deposits were formed, 

 protecting the shell-residues in places. When the local 

 glaciers finally began to melt away,- copious deposits would be 

 formed in all the valleys ; the hills would rapidly become 

 reduced in height when the elevatory movements ceased, and 

 their old crags and summits would become represented by the 

 sands and "drifts" of GlencuUen and the plains. These 

 would be full of scratched blocks from the hill- moraines, 

 mingling with those of other glaciers from the north ; stream 

 after stream would mix and redistribute the, materials. The 

 old *' pockets" of shells would be laid bare again, and would 

 be washed down into the general river-drift. While appear- 

 ing on the top of many of the glacial deposits, they might 

 thus bear record of an older subsidence, denudation, as it must 

 do again and again, having rearranged the deposits in the 

 reverse order of their formation. This is naturally suggested 

 to us by the startling resemblances between our "sands and 

 gravels" and the ordinar}^ material that infills the Alpine 

 valleys. GlencuUen is in this respect a model of the northern 

 slope of the Brenner, or still more of the great Drau valley 

 near Sachsenburg and Villach. Perhaps, to understand our 

 "glacial epoch," we may yet have to turn from Greenland to 

 the chains of central Europe, and to reconstruct from the 

 drift-choked vallej^s the former greatness of the hills. 



The winding gravel ridges, or Eskers, of which that quarried 

 into at Balrothery and Greenhills is so beautiful an example, 

 cannot yet be considered as explained. Mr. G. H. Kinahan 

 has made an extended vStudy of them, and inclines to refer 

 them to the action of marine currents during the last slow 

 emergence of the land.' 



Even since the country settled down into something like its 

 present climatic conditions, the changes wrought by denuda- 

 tion have been enormous. The earliest Irish Elks may have 

 wandered upon hills of shale and limestone, abutting on the 

 granite, where now the lowland of Stepaside and Cabinteely 

 stretches. In such high ground Prof. Hull= has sought the 

 explanation of the Scalp, the head of the valley having been 



^ "Geology of Ireland," pp. 226-231. See also "On the Drift in Ire- 

 land," G. S. /,, i., 191, and iii, , 9, for a discussion of many types of Drift. 



"^ Sci. Proc, R. Dublin Soc, new ser., i., 11.; and " Physical Geology of 

 Ireland," 2nd edit., p. 215. To appreciate the argument, the sections 

 should be drawn with the same vertical and horizontal scale. 



