The Senonian series is represented by the White Limestone, a hardened chalk with flints, which is often glauconitic and conglomeratic at the base.
In spite of the bulk of the evidence being in favour of geniality of climate, it is necessary to observe that certain deposits have been recognized as glacial; in the culm of the Frankenwald, in the coal basins of central France, and in central England, certain conglomeratic beds have been assigned, somewhat doubtfully, to this origin.
The remainder and greater part of the county is occupied chiefly by the gently inclined Old Red Sandstone; in the dissected plateau of the Black Mountains north of Crickhowell the lower marls and cornstones are laid open, while south of Brecon the conglomeratic upper beds form the escarpment and plateaus of the Beacons.
The sea grew shallow, the deposits became conglomeratic and shaly, volcanic eruptions began, and the present folds of the Apennines were initiated.
Certain conglomeratic beds on which Armagh is built are also believed to be of Permian age.
The Senonian limestone itself, which rests in the extreme north on Trias or even on the schists, is often conglomeratic and glauconitic at the base, the pebbles being worn from the old metamorphic series.