Calp

Notes:

A dark, mud-bearing limestone with thick beds containing internal thin flat or convoluted laminations. It was probably deposited in deep water marine settings from sediment that was carried from shallow water down-slope by turbidity currents. Calp contains between 25 and 30 weight % of insolubles, mainly clay (Marchant and Sevastopulo 1980, p. 202) and sometimes a small volume of the iron sulphide mineral Pyrite or "Fool's Gold", which may form small cubic crystals. Generally poorly fossiliferous, it contains some brachiopods, bryozoans, sponge spicules and foraminifera. Often small, thin, white veins of quartz or calcite cross-cut the foliated fabric of the stone. The term "Calp" was coined by the celebrated Galway chemist and mineralogist Richard Kirwan. Although the type locality is in Dublin, Calp is widely distributed in Ireland.

'The calp limestone is so called from a name accidentally given to the very extensive beds of impure limestone and shale which prevail in the counties of Dublin, Meath, Longford, Donegal, Sligo &c. It differs from the ordinary Carboniferous limestone, in its being generally of a dark colour (though sometimes of a pale, ashy appearance), and in its alternating with beds of clay and shale; and it commonly contains a large proportion of silex, which renders it hard, and brittle in fracture, and frequently very difficult to work. It produces large, flat-bedded stones, which, however, are seldom of much thickness; except in the county of Donegal, and the surrounding district, it occupies a low, comparatively level surface, from which circumstance the quarrying of it is often attended with difficulties, from the quantity of water with which the quarries become filled.' (Wilkinson 1845, p. 37).

Beds of the calp limestone were extensively used in the construction of the Shannon Navigation, but the quality of the lime varied within limited areas, even within the same bed (Wilkinson 1845).