April 1, 1898.] 



KNO^A/•LEDGE 



75 



see the mists clearing from the granite peaks of Mourne, 

 and the saw- edge of the Carlingford range already black 

 against the sky. And we look farther up the sea-lough 

 towards Newry, where the ground rises inland to form the 

 plateau of Armagh, bearing on its back the volcano of 

 Slieve GuUion and other giants of the moorland. 



To reach Belfast, again, we pass up the lough between 

 the hills of Down and the far bolder and terraced masses 

 of the Antrim coast, and rest at last against the quay, 

 where the smoke of a busy commercial centre cannot blot 

 out the great black crags that rise almost sheer above the 

 town. 



Or, again, near Cork, where the foreground is lower, and 

 something in the pleasant Falmouth style, glimpses are 

 seen of those fine red-sandstone ranges that run from 

 Waterford to Kerry, and form a backbone to all the 

 southern coast ; while an approach from the Atlantic 

 side, to Bantry, Cialway, or Donegal, would impress still 

 more firmly on the traveller the mountainous nature of 

 the country. 



Yet, start this traveller by rail from Gal way to Dublin, 

 or from Cork to the sea again at Drogheda, and he will 

 report that Ireland is a Hat country, with occasional 

 bands of mountains on its margins. In the former case 

 he will cross the Shannon in a broad prairie at Athlone, 

 and will hail even the little gravel-ridges as welcome 

 features in the plain. In the latter case he will pass the 

 lordly range of the Galtees, and will have visions of the 

 long chain of the Leinster granite between him and the 

 eastern sea ; but his course will lie through a pleasant 

 cultivated lowland, with white farms and foursquare 

 mansions, and anon stretches of brown bogland, margined 

 by wind-swept belts of firs. The structure of Ireland 

 seems, then, fairly simple — a shallow basin, bordered for 

 the most part by a rim of higher ground. 



The details of its structure have been put before 

 geological readers in two well-known works ; and, in a 

 more popular setting, by von Lasaulx,^ who visited the 

 country in 1876. Gne of the most charming accounts of 

 Ireland, and the most fully illustrated, is to be found 

 in the work of another foreign author, M. Martel ; ; and 

 the geological matter in this book is unfamiliar to most 

 of us, dealing as it does with the underground water- 

 ways of the Carboniferous Limestone area. In this and 

 succeeding papers, I propose to regard Ireland from a 

 broad standpoint, as a part of Europe, as a mass set 

 upon the continental edge — that is, upon one of the most 

 interesting structural lines of Europe at the present day. 



Bertrand and Suess, the authors of our more recent 

 generalisations respecting European structure, have not 

 overlooked Ireland as the visible western termination of 

 their systems of earth-folding ; and the latter writer may 

 be said to show an intimate acquaintance with the geology 

 of the island. M. Bertrand; has recited to us the four 

 principal epochs of mountain-making, and has somewhat 

 daringly pictured the folds as successively extending south- 

 ward, banked one against the other, from the Polar Circle to 

 the Mediterranean. Certainly, the bared Arch:pan masses 

 of the north, and the growing limb of the Italian region in 

 the south,;; go far to support his generalisation. 



* Gr. U. Kinahan, " Manual of the G-eology of Ireland," 1878 ; and 

 Prof. E. Hull, " Physical Geology and Geography of Ireland," Second 

 Edition, 1891. " 



t "Aus Irland : Keisestizzen und Studien," Bonn, 1878. 



'X "Irlande et Cavernes anglaises," Paris, 1897. 



§ " Sur la Distribution geographiques des Roches eruptires en 

 Europe." Jiull. Soc. giol. de France, Troisieme Serie, Tome XVI. 

 (1887-8), p. 576. 



i; See Knowledge, Vol. XX. (1897), p. 2S5. 



Ireland, as an epitome, retains traces of these four great 

 epochs. In the mountain-rim of the north and west, the 

 oldest system of folds, the Ihironiaii chain of Bertrand, 

 comes to light. Complex as the older rocks of Donegal 

 may be, few will deny that their fundamental series is of 

 equal antiquity to the Hebridean gneiss of Scotland ; while 

 an interesting inland exposure in the east of the county of 

 Tyrone shows that ribs of the pre-Cambrian chain are not 

 far distant beneath any part of the north of Ireland. The 

 handsome gneisses of this latter area, north of Pomeroy, 

 form a broken moorland, to which echoes of the outer 

 world travel slowly even in our own time — a region in 

 which the old language, and the lirightness of the old 

 costumes, linger almost witliin sound of the clanging ship- 

 yards of Belfast. Flanking this core of antique rocks, come 

 interpenetrating masses of igneous origin, and an extensive 

 series of schists that form mountain-ridges of their own. 



In the counties of Mayo and Gal way, again, the strati- 

 fied but metamorphosed series that underlies the first 

 fossiliferous horizons is now known to be at least of 

 Cambrian age ; and its general relationships would 

 carry it down even further. The quartzite masses of 

 the Twelve Bens of Connemara may even represent the 

 Torridon series of Sutherland : and somewhere beneath 

 them must lie the gnarled and twisted gneiss, forming 

 part of the continent of " Huronian " times. South of 

 this point the old rocks are cut off by the Atlantic, and 

 play no further part in the structure of our modern 

 Ireland. 



The ('al<-tl<mian epoch of mountain-building set in at the 

 close of the Silurian period, and gave us the Grampian 

 folds, and the great thrust-planes that have wrought such 

 havoc with the true order of things in north-west Suther- 

 land. f It gave strength and compactness to a great part 

 of Wales ; and its first throes are seen in the break that 

 occurs between the Ordovician and the Silurian beds in 

 Shropshire. On the Welsh border, iu fact, the Caledonian 

 movements made a start a whole geological period in 

 advance of the main upheaval of the chains. 



Evidence of something of the kind is now reported from 

 the west of Ireland; but the principal folding in that 

 country certainly included Silurian beds as well as Ordo- 

 vician. Along the east coast, from the neighbourhood of 

 Belfast to the south of the county of Waterford, the 

 Caledonian pressures have thrust up these two systems of 

 beds on end, and have contorted or even inverted them. 

 From the mountains and plateaux then raised, pebbles 

 were copiously rolled down, to form the first deposits in 

 Devonian lakes, or, later, in Carboniferous seas. In fact, 

 a continent then arose across all the northern European 

 area, on which room was found for the fresh-water basins 

 of the Old Red Sandstone, and on the mobile edge of 

 which the volcanoes of the Cheviots fumed. 



The surface of this continent is, then, exposed to us 

 by denudation whenever the Devonian conglomerates are 

 removed ; and certain portions of it must have stood up 

 as barriers between the lake-basins, and were never sub- 

 merged until the great subsidence, which readmitted the 

 sea in early Carboniferous times. 



The great thickness of the Old Bed Sandstone implies 

 that the floors of the lakes in which it was deposited, 

 or of the estuaries that may have served in certain 

 oases as the gathering-ground, were steadily sinking as 



* This, at least, may be safely concluded from the most recent 

 results of the Geolog"ical Survey in that district. fAnn. Report 

 GeoL Surrey of United Eini/dom. 1897, pp. 50 and 51.) 



t See the sections in the Survey. Report published in Quart. Joiirn. 

 Geol. Soc, London, Vol. XLIV. (18SS\ p. 378. 



