294 Paleo-Geological and Geographical Maps of the British Islands. 
In Ireland the upper boulder clay, resting on the marine gravels of the interglacial 
stage, has been noticed in several places, as at Killiney near Dublin, along the 
Wexford coast,” at the marble quarries near Kilkenny,t at Modabeagh colliery near 
Carlow,{ and in Counties Tyrone, Antrim, and Derry. It is similar to its English 
representative, but has probably suffered more from denudation, so that it is only to be 
found in small detached areas. When it was in course of formation the land was in 
places probably depressed to a level of about 1,000 feet below that it now occupies, 
and as the sea-bed still further rose, the soft material of which it was composed 
would have offered but slight resistance to the waves and currents which chafed 
around the unprotected prominences. In more than one instance which has come 
under my notice, the formation would seem only to be represented by blocks of 
travelled stone stranded on the surface. An instance of this kind occurs at 
Kilkelly, in Co. Mayo, where large slabs of Carboniferous grit are to be found 
strewn over a tract of country of considerable extent, covered by a thick deposit 
of gravel on which these blocks are found resting.§ 
When we turn to Scotland we are met by difficulties: of identification, as the 
geologists of that country do not seem to have recognised a representative to the 
Upper Boulder Clay.|| Dr. J. Geikie refers to the “ Upper Drift Deposits,” very 
diverse materials, such as coarse, earthy débris of angular fragments, and large 
blocks and boulders which are strewn over the northern slopes of the southern 
uplands. These he traces to the Grampians as their source, and considers they . 
have been brought to their present position on a second great sheet of ice moving 
southward. It is, of course possible that the more northerly positions, the greater 
elevation of the Grampians and North Highland mountains than those of other British 
districts, and the consequently greater amount of snow and ice which must have 
accumulated on their summits and slopes, may have produced a second ice sheet 
which has no representative elsewhere ; and in such a case, the central valley, though 
really below the sea level, and submerged to a depth perhaps of several hundreds 
of feet, may have been completely filled with ice, which for a time excluded the 
waters of the sea. But admitting all this, it is inevitable that when the ice began 
to give way, owing to the approaching amelioration of the climate, it would be 
* Professor Harkness, ‘“ Geol. Magazine,” vol. vi., p. 542. 
+ “Phys. Geol. Ireland,” p. 90. Geikie, “Great Ice Age,” 2nd edit. 
+ Hardman, Journ. Roy. Geol. Soc., vol. iv., p. 73; Expl. Mem., Sheet 35 of the Maps Geol. Survey. 
Here the Upper Boulder Clay was proved to be 84 feet in thickness, resting on 25 feet of sands, gravels, 
and clays, and this again on Lower Boulder Clay 8 feet. The elevation is about 750 feet. 
§ Originally described by Sir R. Griffith, Brit. Assoc. Rep. 1844. 
|| My own observations in the Glasgow district, however (1868-9), lead me to think that such a deposit 
may occur east of that city. 
@ Loe. cit. 
