257 
Geological Relations of the East of Ireland \ 
clay, calp, or swinestone, or where it abounds in lydian stone. 
The black limestone, in the latter case, is a hard compact rock, 
often of a siliceous nature, requiring much fuel for its conversion 
into lime, and from this cause sometimes unfit for the purpose. 
It may frequently be observed in Westmeath, Meath, Dublin, and 
Kilkenny. 
Calp may be considered as an intimate mixture of limestone and 
slate clay yet perfectly homogeneous in aspect, it seems as much 
entitled to the rank of a species as many other minerals which are 
placed under that title in systems of mineralogy. It forms the 
common building stone of Dublin, and may be seen to advantage 
in the quarries at Crumlin, where it alternates with slate clay, in 
beds varying from one to three feet thick, dipping gently toward 
the south. The common associate of calp is slate clay, sometimes 
containing imbedded spheroidal, or lenticular masses of clay iron- 
stone; but the purest limestone strata are continuous, and free 
from slate clay or other beds. The foreign beds of these sub- 
stances abound more particularly in the eastern quarter of the tract 
toward the coast, in the counties of Meath, Dublin, and Kildare ; 
while, in the interior of the field, the more usual associates of the 
limestone are lydian stone, hornstone, or flinty slate, imbedded in 
isolated portions, or in alternating layers. The structure of the 
limestone varies, throughout the tract, from the perfectly compact 
to the conjointly compact and foliated, and even granularly foliated. 
Beds of the last kind are quarried and wrought for various pur- 
poses in the northern parts of Westmeath, and also near Tulla- 
more in the King’s county ; being of a greyish white colour, and 
of a large granular texture. 
The limestone, when . associated with calp and black limestone, 
passes sometimes into the state of swinestone, and in those portions 
Vol. V. c 2k 
