584 Scientific Proceedings, Royal Dublin Society. 



Walk Mills. Three miles east and south-east of Limavady. — 

 Brownish and reddish flags, from 3 to 5 inches thick. 



Triassic. — Reddish and orange ; locally called " Eed Free ; " 

 very easily worked, but friable, and in general not durable ; used 

 locally. 



Jurassic. — Thin-bedded sandstones occur as subordinate layers 

 in the band of Lias that margins in places the Cainozoic plateau 

 of Antrim dolomyte. They have been used as flagging, but are 

 soft, and liable to get damp. Formerly they were in great request 

 as scythe stones, a considerable trade in them having been carried 

 on at Magilligan. 



Cretaceous and Eocene. — The arenaceous adjuncts of these 

 rocks are the Flints and Agates, the latter occurring principally 

 in the lower Eocene Conglomerate. Anciently they were wrought 

 into war implements. They have been previously mentioned in 

 the description of the Co. Antrim (page 534). 



Sand and Gravel. — Good pit sand, if well selected, can be 

 procured near Coleraine, and Magherafelt, in Bishop's Demesne,. 

 Derry, and in the vicinity. Good river sand is found near Derry 

 and near Newtownlimavady, being very good along the Eiver Roe. 



A fair quality of sea sand is procured from the sand-banks at 

 Magilligan. 



In Londonderry, in 1820, a glass manufactory was established 

 in the old sugar refinery, Sugar-house-lane, but was closed after a. 

 few years. It is not now known where they got their sand. 



LONGFORD. 



To the north of the county, coming in from Leitrim and Cavan, 

 are Ordovicians, which are margined by Loiver Carboniferous Sand- 

 stones. At Granard, however, there are peculiarities, the sandstones 

 being interstratified with the limestones. In the neighbourhood 

 of Longford also, south-west of Ardagh, there are outlying expo- 

 sures of Ordovicians associated with more or less marginal belts of 

 Carboniferous Sandstone ; while in the Calp there are also arenaceous 

 rocks, some of which will be mentioned. 



Ordovician. — Here, as elsewhere, the grits and sandstones do 

 not seem to be known, except locally, as none of them appear to, 

 be eminently suited for cut-stone purposes. 



