84 REPORT — 1875. 



Kilkeel aud Whitewater rivers. This district, lying' to tlie S.E. of tlie Mourne 

 Mountains, across Avbich the ice-ilow came from the N.N.W. and N.W., though 

 obstructed and deflected, yet passing over elevations of at least 2000 feet, is covered 

 by deep accumulations of drift, excellent sections of vrhich are exposed iai the river 

 and sea-escarpments, some up to 120 feet in thickness. In these were seen the 

 lower boulder-clay, or genuine till, restmg on the denuded and often glaciated 

 surfaces of the Silurian rocks, with subangular, rounded, and ice-scratched blocks 

 firmly imbedded in a brownish clay, the lowest portion being chiefly a blue clay, 

 and containing shells, mostly fragmental, those identified being TurriteUa com- 

 munis, Bticcimim undatinn, Leda rostrata. Overlying this boulder-clay in the above 

 cases, and as illustrated in diagrams, were the " interglacial saTids and gravels," 

 mostly horizontally bedded, and often forming extensive flat-land surfaces. Over- 

 lying these in places were accumulations of in-egularly bedded gravels. 



In the county Mayo, near Ballycastle, a section in tlie Glenulra river, 120 feet 

 in depth, showed on top irregularly bedded coarse gravels for 25 feet, then evenly 

 bedded fine gravels and sands for 30 feet, containing shell fragments, below which, 

 though graduating from it, was some 50 feet of lower boulder-clay, the lowest part 

 being a stifle plastic blue clay ; in these, especially in the latter, the shell fragments 

 were very abundant. In several localities adjacent, particularly in the stream 

 Fiddawntawnanauneen, the specimens obtained were both numerous and very per- 

 fect; those identified were 'Tel/ina pro.rhna, Cyprina islandica, and a Balanus. The 

 author, without wishing to theorize on these deposits, wished only to add a few 

 facts to the general store of knowledge regarding our drift deposits. 



On a Mass of Travertine or Calcareous Tuff, called " The Glen Rock" near 

 Ballycastle, County Mayo, Ireland. By William A. Traill, M.A.I. 

 {^Master in Engineering), F.R.G.S.I., H.M. Geological Survey of Ireland. 



The district in which this rock occurs is situated on the northern shore of the 

 county Mayo, the rocks of the country consisting of Carboniferous sandstones and 

 limestones," viz. white, brown, yellow, and red sandstones, with bands of shales, 

 and pure and impure limestones, mostly inclined at low angles E.N.E. In that 

 district several stalactite formations and deposits of carbonate of lime occur, the 

 largest being "The Glen Rock," about two miles from Ballycastle, a mass of 

 calcareous tuff" and travertine resting on the easternflanksof the valley along which 

 the limestone beds crop out, approximately of the following dimensions : — length 

 N. and S. 310 feet, E. and W. 285 feet, and in depth or thickness from G to '80 

 feet. The mass is irregular, and in cubic contents about 2,100,000 cubic feet. The 

 tuft' varies from a soft porous nature to a hard ringing travertine, and is composed 

 chiefly of the casts or incrusted forms of diverse vegetations, of brambles, ferns, 

 grasses, and ivy. Sec, and containing the bones of birds and small animals, aud 

 shells of land-snails, &c. The origin of this large mass must be attributed to a 

 large spring or " Holy Well," situated a little above on the slope of the hill. The 

 water, by its passage through the limestone rock, becoming highly impregnated 

 with lime, and by flowing over the vegetation on the slopes, has encased and 

 cemented them together, and produced a much more vigorous growth, thus more 

 rapidly building up this isolated mass of tuft", which stands out as a striking feature 

 throughout the valley — the age of this mass being, of course, quite recent, after 

 the present conflgTiration of the coimtry had been formed. There are evidences, 

 however, that it has not increased in thickness for the last 300 years, as foundations 

 of that age still exist on its highest summit ; but now it seems to be rather break- 

 ing up under its own superimposed weight. 



For upwards of twenty j'ears a school was held in a natural cave in this rod:, 

 enlarged for the accommodation of sixty scholars, but which was closed in 

 the year 1815. Since then the roof has subsided, filling it up for the most 

 part. Various traditions connected with this rock were also noted, and specimens 

 exhibited. 



