Geology in Limerick
Around Limerick (Self Catering, Limerick, Ireland) and extending south-eastwards for some 20 miles is a large area in which is displayed abundant evidence of volcanic activity during Car- boniferous times. The lavas and ashes have resisted the action of the weather better than the limestone which envelops them, and thus they form a series of low hills which are rendered conspicuous because of the flatness of the surrounding country. The old castle of Carrigogunnel, 5 miles west of the city, stands on one of these igneous masses. Caherconlish is another large exposure, whilst about Pallas Grean and Herbertstown they are developed in an almost continuous zone. The Carboniferous rocks may be divided into four groups. Given in order, the earliest being below, they are :
Coal Measures.
Millstone Grit.
Limestone.
Shale.
The Shale is found commonly at the sides of the valleys in the south of Ireland, and generally as a thin band surrounding the exposures of Old Red Sandstone. In the south of Cork is a large area of Carboniferous Slate which represents a much longer epoch than that in which the Lower Limestone Shale of the rest of the country was formed. With the slates arc. associated the Coom- hola Grits which are found well developed on Shehy mountain north-west of Dunmanway. Limestone occupies the valleys from that of Cloyne northwards. Tongues of this rock extending from the Central Plain envelop the Galtees, one pushing through by Charleville to Mallow, the other reaching round by Caher and Mitchelstown. Six miles east of this latter place are the well-known caves. These were formed by the solution of the limestone, and in them are many
beautiful columns made by the coalescence of stalactites suspended from the roof with stalagmites formed on the floor below.
The loose ice-borne material or drift, from which is derived most of the soils of the cultivated lands, is throughout most of the province similar to the debris of the rocks upon which it rests, and thus there is little difference between the derived soils in the two cases. An exception occurs in the soils at the head of Bantry Bay. These are greatly enriched by the limestone boulder clay. A similar enrichment is found to follow the presence of this type of boulder clay in the vicinity of the Silurian hills of Tipperary, whilst the Vale of Aherlow and the Golden Vale of Limerick owe their wealth of soil to the large proportion of limestone and volcanic rocks in the mixed materials of the drifts in those places.