124 Revieics — Prof. Hull's Physical Geology of Ireland. 



characters of the Old Red as a formation insisted on. This vast thickness of sand- 

 stones, conglomerates, and slates appears to have been thrown down in the waters of 

 a large lake or great inland sea, as first pointed out by one to whom English geology 

 is largely indebted for broad philosophical speculation in its physical history, Mr. 

 Godwin-Austen (not Austin as printed), or rather in two lakes separated by a great 

 ridge of Silmian land crossing Ireland, and what is now the Irish Channel, into North 

 "Wales and Central England, though in all probability the basin formed to the south 

 of this ridge did not extend so far in the south-east. In the northern area the 

 rocks have much the same character as their representatives south of the Grampians 

 and in Central Scotland ; but in the south and south-west the formation shows two 

 distinct members — the upper of which (essentially Irish) very distinctly passes into 

 the Carboniferous rocks above, the lower forms the greater portion of the extensive 

 counties of Cork and Kerry, and forms some of the most elevated ground in Ireland. 

 About one-half of the entire area of Ireland is occupied by rocks of the Car- 

 boniferous series, chiefly confined to the lowermost members, the Carboniferous slate 

 and the Carboniferous limestone. This latter, which was with justice called the 

 Mountain limestone in England, ought more properly in the sister-isle to be called 

 the Plains limestone, because, excepting in parts of Leitrim, Sligo, and Fermanagh, 

 where it rises into bold isolated hills and escarpments, it is found only under the 

 wide-spreading plains of the country. The Upper Carboniferous beds, including 

 some of the Coal-measures, are now only represented in a few detached areas, 

 barely sufficient to mark the former widely- extended area of the formation. The 

 Carboniferous Limestone itself presents in Ireland three acknowledged divisions. 

 (1) The Lower Limestone, generally a pure, fossiliferous limestone, many of the 

 beds yielding richly-coloiired and handsome marble ; (2) the Calp, a dark-coloiu-ed 

 earthy and shaly series ; and (3) the Upper Limestone, often of a lighter grey colour 

 than the lower, and often full of "Chert," both in irregular layers and masses like 

 the flints in chalk. Volcanic rocks occur in places, showing the existence of such 

 action during the deposition of these rocks. Representatives of the " Yoredale beds," 

 and of the " Millstone-grit" of England also occur; as well as of the '' Gannister 

 beds." Of the Upper Coal-measures, whatever may have been their original extent, 

 there now remain only two or three very limited areas, as at Castlecomer in the 

 counties of Carlow and Kilkenny, and Killenaule in Tipperary (which may be 

 considered parts of the same general area) : and at Coal Island in Tyrone. 



Permian rocks have only been recognized in a few places ; the Lower Permian 

 only in one ; viz. a few feet of conglomerate and breccia resting on the Lower 

 Carboniferous Limestones of Armagh. The Magnesian Limestone is represented, 

 though poorly, near Cookstown in Tyrone, and at Cultra, on the south shore of 

 Belfast Lough. 



Of the Mesozoic rocks, as already stated, no representatives are known in any part 

 of Ireland, excepting in the north-east ; there the Triassic rocks form a narrow 

 band, encircling the basaltic region of Antrim and East Derry, generally occurring 

 in the lower ground of river valleys. The two groups of the Bunter Sandstone 

 and Keuper are both recognizable, the former chiefly in Belfast Lough and near 

 Dungannon, etc., and the latter between Larne and Carrickfergus, marked by the 

 presence of bands of gypsum and extensive beds of rock-salt (Carrickfergus). At 

 Scrabo, near Newtownards, the Triassic sandstones are capped by masses of dolerite, 

 and are also penetrated by horizontal sheets, and vertical dykes of basalt, intersecting 

 each other in various directions, and affording a magniflcent opportunity for the 

 study of such phenomena. 



The Lower Liassic and Rhsetic beds occur together in a few places round the north- 

 east coast, as at Colin Glen, near Belfast, Larne, and Portrush ; at the latter locality 

 indm-ated and converted into a kind of Lydian stone, by contact with a sheet of 

 intrusive dolerite. At Larne the beds are of light blue and deep grey clays, with 

 earthy limestone, containing Gryphcea incurva, etc., and below these dark shales with 

 ^vicula contorta. 



There are no representatives of the main portion of the Lias of England, nor of 

 any of the numerous divisions of the Jurassic rocks, as yet known in Ireland. They 

 very pirobably were never deposited ; but if they were, they had been entirely removed 

 again before the period of the formation of the Upper Cretaceous rocks. For there 

 is no representative of the lower part of this great series either ; we find only the 

 Upper Greensand and the Chalk with flints. The whole group varies in thickness, 

 but never exceeds a maximum of about 350 feet. The upper surface has been 



