Cou7ity D2ibli7i, Past ayid Presertt. 91 



taceous beds formerly extended farther west ; and we have no 

 proof that the sea in which they were deposited did not flow 

 along the south of Wales and away into south-central Ireland. 

 Similarly, the Antrim chalk may have had a verj^ wide exten- 

 sion. A shore-line was undoubtedly near in the north and 

 west; but, so far as Co. Dublin is concerned, it is open to 

 anyone to assert that the uptilted Carboniferous masses again 

 sank beneath Mesozoic seas, and were again uplifted and ex- 

 posed to denudation during the volcanic period that intro- 

 duced the Tertiary era. 



Both the Mesozoic and Cainozoic (Tertiary) eras are, in fact, 

 almost a blank in southern and central Ireland ; and we pass 

 directly from the Carboniferous period to some of the most 

 recent deposits with which the geologist has to deal. 



On the banks of the Dodder and its tributaries, or on the 

 east of the Sutton strand, or at the top of the quarries near 

 Finglas, to mention no other sections, coarse gravelly mate- 

 rials, often roughly stratified, are seen to form the present 

 covering of the country. They fill the hollows worn pre- 

 viously in the old hard rocks, and lie unconformably across 

 Carboniferous, Ordovician, or the slates of Howth and Bray. 

 In some of these loose deposits marine shells may be found, of 

 species still inhabiting the Irish seas or slightlj^ more northern 

 waters.' The once famous section at Killiney has been much 

 affected by the railway^ and by vegetation ; but similar beds 

 form the shore-line south of Bray Head, being finely exposed 

 between that point and Greystones. Where the shells are in 

 fair condition and the deposit fringes the present coast, we 

 may expect it to be a *' raised beach," the evidence of the last 

 elevatory movements of the district. The officers of the Geo- 

 logical Survey thus state that *' the gravel terrace of Sandy- 

 mount and Merrion is probably the most southern remnant of 

 the raised beach. Along the valley of the Liffey it merges 

 into the alluvium of that river, forming the level ground occu- 

 pied by the buildings of the University of Dublin, of Dame- 

 street, Sackville-street, and the north-eastern suburbs of the 

 city." 3 



But when recent marine shells are found at far greater 

 heights above the sea, in the sands and gravels of the moun- 

 tains themselves, it is clear that we are dealing with a different 

 order of deposits. Dr. Scouler^ at an early date recorded 



^ See T. Oldham, " On the more recent geological deposits in Ireland," 

 G. S. D., iii. (1844-5), 66, 69, and 131; J. R. Kinahan, "Drift Fossils from 

 Bohernabreena," G. S D., viii. (1858), p. 87. 



2 See warning by Mr. G. H. Kinahan, G. S. /., iv., 118. Also for very 

 valuable comments as to the relative ages of loose drifts, " On the 

 classification of boulder-clays and gravels," G. S./., vi., 270, by the same 

 author. 



3 Memoir to sheets 102 and 112, 2nd edit., p. 70. 



^" Elevated hills of Gravel containing Marine Shells, in the County of 

 Dublin." G. S. D., I (1838), 275. 



