ii§ The Irish Naturalist. May, 



geolog}'. That the distinguished District-Geologist and his 

 limited staff have accomplished so much in a complex district 

 in the limits of a single year is strong testimony to the 

 efBciency of the Survey, acting under the stimulus of high 

 ideals. In work such as this, the question is one of accurately 

 recording what is seen on the surface of the ground ; but the 

 geological map must not be merely petrographic, like that of 

 an economic soil-surve}'. It must convej^ to the mind the 

 conclusions of those who have every right to form a judg- 

 ment ; it must correlate certain deposits, and divide others on 

 grounds of differences in age or conditions of formation. In 

 this case, the map and its marginal index serve almost as a 

 text-book ; to confirm or criticise the conclusions expressed 

 by it, we may take up the accompanying Memoir and sally 

 forth to the localities indicated in its pages. 



lyCt us take the map, howe\^er, for a moment by itself One 

 of the most striking features is the mass of drift, sand and 

 gravel, limestone, boulder-clay, and non-calcareous cla}-, 

 banked against the mountains in the south. The deposits run 

 high up into the pre-glacial hollows ; later downwash from 

 the slopes has crept over some of them, and a sprinkling of 

 granite boulders rests on others. The sands and gravels of 

 glacial mounds and eskers are, on structural grounds, distin- 

 guished from those intercalated in boulder-clay ; the deposits 

 below Tibradden are of the former character, while those of 

 Killiney cliff are of the latter. We then trace the action of 

 rivers on the general coating of the countr\' ; the terrace- 

 gravels of the Liffey, the Dodder, and the Rockbrook streams, 

 are clearly marked out in colour. Here at Willbrook is an 

 expansion due to early flooding; in other places, notably 

 along the grassy flats of the Liffey, recent alluvial infilling has 

 tended to fill up the floor between the terraces. Here,, again, 

 the Dodder is vStill cutting a little gorge, and limestone 

 appears along its course near Milltown ; while at Donnybrook 

 it emerges on its delta, which, as the stippling informs us, has 

 been raised in faiily recent times above the sea. The modern 

 intake between the Custom House in Dublin and the sea is 

 separately indicated, outside the shore-line of 1673. ^^^ island 

 is shown as having existed at that date, in place of the now 

 continuous sand-banks of Clontarf A still more modern 



