December, 1902.] 



KNOWLEDGE. 



283 



It is hard to believe tliat the strivts of Dublin lie only 

 seven miles away in the f^reat limestone j.lain ; and Dublin 

 has always known and felt the nearness of the Leinster 

 moors. Even to this day, the coast and [lort, and the 

 lower valley of the LifFey, are largely held and worked by 

 men of l-'nglish names ; the highland that calls us i>ut from 

 Dublin at the end of each southward-stretehiug avenue is 

 still, to all intents, the land of the O'Tooles and the 

 O'Byrues. 



The mouth of (he Liffey, and the deltas of old glaeial 

 gravel along the shore, were an obvious temptation for 

 the Norsi' invaders. After plundering the islands, the 

 sea-kings grew bold and settled on the land ; they found 

 Dublin a group of green ratlis guarding a river-ford, and 

 they made it a busy port and city. None but a sea-faring 

 people need have used Dublin as their capital. The 

 central Irish fell on it from time to time, and- the 

 Scandinavians sought safety in alliance with the hill-men. 

 Even Brian, after a month of plundering, left the city to 

 be reocoupied by the enemy ; to be king in Ireland was to 

 be lord of the great central ]ilaiu. And thus it came about 

 that the Normans, in 117(1, took Dublin from their old 

 Norse kinsfolk rather than from the Irish.* From first 

 to last, Dublin was a stronghold of the stranger. 



Strongbow's Normans, with his southern allies, actually 

 sur{)rised the city by coming down on it across the granite 

 hills. ()ut of the same hills, and creeping through the 

 ■woodland, on a fatal day forty years later, the O'Byrnes 

 and O'Tooles in turn fell on the men of Dublin. Two 

 hundred years passed, in which the English forces were 

 again and again broken on the highland, and still a 

 battle had to be fought at Bray, at the seaward end 

 of the landscape we have just described, where the 

 O'Bvrnes were taught for a time to regard the limits of 

 the Pale. 



"Within their highland, however, they were always safe 

 enough. The great fight in the ravine of Glenmalure, 

 where Lord Grey's army was shot down by hidden 

 musketry, reads like an Elizabethan version of some 

 mishap in the late Boer war. In l.'J91, again, young 

 Hugh Roe O'Donnell lied from his prison in Dublin 

 straight to the iinconquered hills ; and few will grudge 

 him his successes of the next ten years. In the bitter and 

 unreasoning days of 1798, six centuries after Strongbow 

 captured Dublin, the Backbone of Leinster was still to be 

 reckoned with, as the natural rival of the plain. 



Strangely enough, and yet appropriately, the denuding 

 forces of rain and rivers, and the storm-winds that swirl, 

 from south-east or south-west, round the northern angle 

 of Slieve Roe, are still bringing to light the features of 

 an older Ireland. Eras ago, the region was covered by 

 the muds of a Silurian sea, and graptolites possessed what 

 now is solid land. Then came the great stresses of the 

 Caledonian folding, and the beds were crumpled from 

 south-east to north-west, in common with those of Wales, 

 the Lake District, and Scotland. Judging by the features 

 laid bare in the Scotch Highlands, and to some extent 

 repeated in Donegal, this epoch of earth-movement 

 produced veritable mountain-chains. The mass of up- 

 heaved sediment was at any rate sutficient to allow of the 

 consolidation of giunite beneath its arches as it came to 

 rest ; while the upward folding went on, the igneous 

 magma followed, and occupied the hollows of the rising 

 chain.t 



* See Joyce, "A Short History of Ireland," 2nd ed., pp. 207 and 

 256. 



t Compare SoUas, " Q-eology of Dublin and its Neighbourhood," 

 Proc. ami. Attoc., Vol. XIII. (1895), p. 107. 



This profound change in the geography of the Britisli 

 area occurre<l without obvious warning. It is true that 

 volcanic eruptions had converted the Welsh Sea into an 

 archijielago in Ordovician limes, and cones were spouting 

 out lava and scoriie both north and south of the site of 

 Dublin. But the Gotlandian (Upper Silurian) period had 

 been far more peaceful. One little volcano ex])loded in 

 the west of Kerry, where its tutfs and agglomerates are 

 brilliantly seen at the present day ; but the sea-Hoor 

 showed no sign of upheaval till near the end of the period, 

 and the ash. beds of Ordovician times were already safely 

 buried in marine deposits. Then came the great waves of 

 the earth's crust, rising in some places only to subside 

 again, but in others perpetuated, where they struck on 

 some resisting mass below. An old north-western Anha'au 

 continent probably provided the obstacle in our area; and 

 Cambrian, Ordovician, and Gotlandian beds were thrust 

 against it, and were pressed over one another as the waves 

 continued to advance. Forced uj) l)y the same earth- 

 pressures, molten matter flowed in from below, attacking 

 the walls of its caldrons and oozing into every crevice. 

 When this matter ultimately cooled, the long anticlinals 

 remained supported by solid granite cores. 



This was the state of things when the Devonian lakes 

 began to gather in the hollows of the land. A certain 

 settlement of the ground assuredly went on, since no new 

 continent can become at once exactly balanced amid all the 

 complexities of the crust. The volcanic eruptions which 

 left such traces in the Scottish Old Red Sandstone, and of 

 which we have hints in Kerry and Tyrone, probably mark 

 the weak lines in the Devonian land. Besides the actual 

 tuffs and lavas, a multitude of dykes, and new intrusions 

 of granite, cut through the Caledonian folds, and show us 

 the dangers to which the continent was exposed. The vast 

 thickness of the Old Red Sandstone indicates, moreover, 

 that the lake-floors were steadily sinking as deposition 

 went on in them. 



Thus it came about that the sea again asserted itself, 

 and marine beaches and mud-flats spread across the 

 Devonian layers. For a long time certain high masses 

 stood out as promontories and islands, and the rivers 

 continued to wear them down, and to add their di'hris to 

 the conglomerates forming on the shore Judging, how- 

 ever, from the occurrence of remarkably pure beds of 

 marine limestone close against masses of Caledonian land, 

 atmospheric denudation was not very active, and the corals 

 and other organisms flourished undisturbed in littoral 

 waters. At the north end of the Leinster Chain we have 

 the most complete pi-oofs, often referred to by geologists, 

 that the denuding forces had already worked down to the 

 granite core. In one or two quarries Ix'tween Dublin and 

 the hills, lumps of granite occur scattered in the limestone, 

 together with flakes of altered Ordovician shale. Some 

 difficulty has been raised as to how these materials came 

 down in isolated patches from the mounti-ins ; but they 

 may rejireseut the last relics of submerged granite knobs, 

 just as banks of subangular gravel represent the lost land 

 off our modern Atlantic coast. The striking Inch con- 

 glomerate in the Old Red Sandstone beds of Kerry, the 

 origin of which is quite unknown, is an extreme example 

 of the same kind. 



The fine black mud that darkens so many layers of the 

 Dublin limestone, and even j)rovides material for bricks, 

 was doubtless also derived from the waste of Caledonian 

 land. The Leinster Chain stood there, then as now, looking 

 down upon the sea, with the quartzites and slates of 

 Howth and Bray forming rugged islets a little to the east. 

 The dead Ordovician volcano of Portrane and Lambay 

 doubtless formed another island to the north, with quaint 



