( 



OF THE BASALTIC FOBMATION OF ULSTER. 87 



formation appears to be the most extensive of its kind in Ireland. 

 Ballintoy is on the coast, a little east of the Giants' Causeway, 

 Lignites occur in many other places within the basaltic area, and 

 occasionally present themselves in the escarpments all round its 

 borders. In no other district, however, have any defined leaf- 

 impressions been detected, and their interest is therefore purely 

 stratigraphical. Wood in a very interesting state of preservation 

 is obtained from the neighbourhood of the Causeway. It is very 

 fibrous, of reddish rust- colour, and almost satiny sheen. The 

 whole tissue has been replaced by oxide of iron, leaving every 

 detail of structure in marvellous preservation. Mr. Carruthers 

 kindly examined it with me and concluded that, unlike all the 

 silicilied wood we have yet seen from Lough Neagh, it is of pine and 

 not cypress wood. A considerable bed of lignite, stated to be six 

 feet thick, crops out in the grand section above the Causeway, and 

 there are ochreous earths at several horizons ; and even so far back 

 as 1836 jS'asmyth found what he took to be charred branches of 

 trees in the red haematite there *. At a place called Lemeneigh the 

 lignite is overlain by compact reddish earth ; and in the not distant 

 bauxite-mine the lignite, five feet thicJ^, is directly overlain by basalt, 

 and rests upon impure bauxite with veins of lignitic matter, then 

 purer bauxite, merging, as at Glenarm, into iron-ore. In the spoil- 

 bank here I found a single impression of a leaf; but though 

 Mr. Swanston and I made every search in the mine, we could not 

 find whence it came. The lignites, iron-ores, and bauxites are here, 

 as elsewhere in Antrim, on practically the same horizon. 



The LougJi-NeagJi Formation. 



The lignitic series of Lough Neagh is very considerable, occupy- 

 ing about 180 square miles, including the entire Lough, except the 

 northern shore between Ballyronan and Sandy Bay. It has twice 

 been bored near Anaghmore to a depth of about 260 feet t, at 

 Portmore to 240, and Dernagh to 173 J, without having in any of 

 these instances been penetrated. Its total thickness can therefore 

 only be inferred §. 



Its composition is similar to that of the Tertiary formation at Bovey, 

 being a mass of alternating white, brown, greenish-blue, and red 

 plastic clays, white and grey sand, with irregular beds of lignite. 

 Judging from the composition of the series it seems probable that 

 it may contain many fossiliferous bands. 



The numerous writers upon it agree in placing its stratigraphical 

 position above the Chalk and beneath the Boulder-clay. It is also 

 believed to rest on basalt throughout a great part of its area, but to 

 overlap and rest on the Trias in the direction of Tyrone. The only 

 two points where it appears to have been actually observed resting on 



* ' Autobiography of Nasmyth,' by Smiles, 1883. 

 t G-rifEth, ' 2nc) Eeport of Eailway Commission/ p. 22. 

 X Hardman, ' Journ. Eoy. Geol. Soc. Ireland,' vol. iv. p. 176. 

 § Hardman, Expl. Mem. to Sheet 35, Geol. Survey of Ireland, estimates theit 

 maximum thickness at not less than 500 feet. Portlock's Eeport, p. 74. 



