The Carboniferous system in West Leinster is almost complete, from the first shales deposited as the sea came in over the Old Red Sandstone, and the still older Caledonian land-surface, up to the Middle Coal Measures, which remain on the high plateau of Laois and Kilkenny. The limestone is for the most part gently folded, and the plain of Offaly and Westmeath no doubt owes some of its character to the approximately horizontal position of its strata. Pro- longed denudation, however, would have in any case produced the same effect, as may be seen where the level surface cuts across crumpled limestones in the counties farther to the east. The plain, largely occupied by grass-lands and stretches of brown bog, is a part of the great Irish peneplain that developed throughout Cainozoic times.
An interesting volcano of Lower Carboniferous age, comparable with the more extensive manifestations near Limerick, lies immediately north of Philipstown. A neck of dolerite stands up prominently as Croghan Hill, South-east of Maryborough, the limestone passes upward into a series of shales and sandstones, which correspond in part with the Yoredale Beds of England. Thin coal-scams occur near the top of this scries, followed by Lower and Middle Coal Measures with more important seams and abundant plant-remains and signs of 
terrestrial conditions. The higher and thicker coal- seams have been well worked in past times ; but a good deal of coal remains below in scams about two ft. thick. The beds are grouped in a synclinal upland, resembling the Forest of Dean, and the highest points occur around tile margin of a depression, in which the town of Castle- comer lies. The Coal Measures of Kilkenny are famous for the remains of amphibians and limuloid arachnids The Armorican earth-crumpling was by no means so severe in West Leinster as in the Cork and Waterford region. The influence of the pre-existing chain of Leinster is seen in the trend of the folds in Laois and Kilkenny, where they run parallel with tile far older Caledonian lines. It seems probable that the whole block of the Leinster Chain was thrust back upon the Carboniferous masses that overlapped it, thus forcing them into folds which repeat those of the earlier series.
The Permian, Triassic, and Jurassic periods are un- recorded in West Leinster, and we have no trace of Cretaceous strata, though chalk may have been laid down here during the overflow that certainly affected a large part of Ireland. The whole Cainozoic era seems to have been one of terrestrial conditions and subaerial wasting, and at the opening of the glacial epoch the surface, both of plain and mountain, was covered with de- tritus and deep soils. Tlie continental type of ice-sheet, spreading across the plain, worked these up into boulder- clay, together with blocks plucked from the rocks beneath, and left a loamy deposit, full of limestone boulders, as it finally stagnated and melted away. The south- easterly and easterly courses of the streams that rail beneath the ice are marked by some of the finest eskers in Ireland. These are conspicuous as steep-sided gravelly ridges, notched here and there by the more recent drainage, in the neighbourhood of Clara and Tullamore, and elongated mounds of the same character form dry areas with swelling surfaces above the boglands of Kildare. A number of Bronze Age remains have been discovered, including the hoard of bronze spear-heads, swords, trumpets, etc., found at Downs in Offaly (Self Catering, Offaly, Ireland) in 1825.
