Kin ah an — Slates and Clays (Bricks, 8fc). 101 



LONDONDERRY. 



Here, as in the neighbouring counties of Donegal and Tyrone, 

 there is a large tract of more or less altered rock, probably equiva- 

 lents of the Ordovician, and perhaps partly of the Llandovery strata. 

 In the less altered rocks the slates and schists range from fine and 

 argillaceous to coarse and arenaceous. Some of the latter, which 

 perhaps are more properly sandstones than schists, and have already 

 been mentioned in the paper on sandstones (vide, p. 581, vol. v.), are 

 largely used for all common walling purposes in Deny and its neigh- 

 bourhood. The principal quarry is at Prehen, where there is a 

 bluish stone, of a slaty structure ; but there are several others, the 

 stones varying slightly in colour and texture. Elsewhere, within 

 the district, the schists and slates are the materials generally used 

 for building purposes ; but they are nearly always unfit for dressed 

 work or quoins. Some contain iron, which soon oxidises and gives 

 a dirty, burnt appearance to the walls. Some of the fine varieties 

 split into coarse slates, and are occasionally used for roofing 

 purposes. 



LONGFORD. 



In the north of this county, in the Ordovicians, at the south- 

 western end of the already-mentioned large tract of these rocks in 

 Cavan, &c, as also in a few small outlying patches, and in the 

 associated Lower Carboniferous, slate rocks occur. These are locally 

 used for walling, similarly as in the adjoining county of Cavan. 



LOUTH. 



Here, as in the adjoining counties — Cavan, Monaghan, and 

 Armagh — there is a considerable area of Ordovicians ; and in them, 

 as elsewhere, there are a number of varieties of slate rock, more or 

 less suitable for ordinary building purposes. In this area slate was 

 used by the old people, as exemplified in the ruins of the ecclesias- 

 tical buildings at Monasterboice, which are constructed almost 

 wholly of them. " The old round tower is a good example of the 

 working of this material, the stones being shaped to the curvature 

 of the circular surface." (Wilkinson.) 



The stones used in Monasterboice seem to have been procured 



