OP THE BASALTIC FORMATION OF ITLSTEE. 89 



" but to remove all hesitation on this head, a man was employed in 

 digging till I could obtain both kinds of wood "*. I was personally 

 prepossessed in favour of the theory that the lignites were the true 

 matrix of the silicified wood, as I have met with partially silicified 

 cores to lignitized trunks at Stafholt, in Iceland, and Cushendall, on 

 the Antrim coast. At my suggestion Mr. Swanston, F.G.S., and Mr. 

 Stewart, F.L.S., both most able observers and much interested in the 

 question, visited Lough Neagh on the 17th November last, and were 

 fortunate enough to obtain evidence which I think it must be admitted 

 sets the question at restt. Their observations are as follows : — 



" IS^ear the ferry across to Rams Island, on the level fringe at margin 

 of the lake, a shallow pit has been sunk, and under about 18 inches 

 of surface-gravel a compact bed of lignite has been struck, and several 

 tons of it thrown out. The material is mostly woody, showing a 

 distinct structure, and seems to have been a deposit of broken drift- 

 wood. Mixed with it irregularly is a good deal of vegetable matter 

 greatly broken up. Twigs can be identified in it, but no leaf -form, 

 although from its flaky character it would seem to be mainly made 

 up of decayed leaves. "We became greatly interested ; and on asking 

 the farmer whether he had found any petrified wood in it, he told us 

 that he had carted some of the lignite to his house for burning, and 

 that the heart of the largest piece turned out to be stone, which he 

 kept, and he was good enough to go with us to the farmstead and 

 give it to us. It was a piece of veritably silicified wood. On 

 examining the heap he had carted, I came on another piece, possibly 

 a fragment of the piece that had been burned, leaving no doubt as to 

 where they came from. The pit has only been sunk to a depth of 4 

 feet, the lignite being compact and undisturbed, but enclosing small 

 patches of white plastic clay." Mr. Swanston further observes that 

 Barton's description is remarkably exact ; for after baling the water 

 out of the pit, he set to work with a spade and dug into the mass. 

 It required great efforts to force the blade of the spade to its fuU depth 

 into it, as it was not of uniform density, the wood being hard and 

 the other vegetable matter more yielding. The lignite appeared to 

 dip towards the Lough 10° or 15° INT. or N.W. The lignites are 

 also cut into at another point north of the Gleuavy river, but the 

 spot is at the present winter-season inaccessible owing to the high 

 level of the water. It seems tolerably evident that the silicifying 

 process only takes place where the lignite is of great thickness and 

 the trunks large and compact. The wood is found most abun- 

 dantly at Glenavy, where these conditions conspicuously exist, as 

 proved by records of borings in the immediate vicinity. Thus 

 Donald Stewart +, emj^loyed by the Royal Dublin Society, says 

 that at Portmore " they bored through two beds of coal, or what 

 is called black wood, 25 feet thick each, and a third 9 feet thick 

 and 80 yards deep ; they bored 18 inches into a 4-feet stratum, having 



* Journal Greol. Soc. Dublin, vol. i. p. 235. 



t Letter from W. S. Swanston, 18th November, 1884. 



i Scouler, I. c. p. 236. 



Q.J.G.S. No. 161. H 



