322 



between two rows of pillars. It is in a place very difficult of access, 

 but the fact, I believe, is so. "What an exhaustless source of specula- 

 tion and conjecture does this furnish to geologists. 



Lignite is got in the cliff over the Giant's Causeway, in the mixed 

 or brecciated layer, between the two columnar layers at that place. 

 The guides show its position. It is from six to eight feet thick. It is 

 accompanied by wacke in thin beds, which alternate with it. 



Doctor Scouler has done good service on this part of my subject in 

 the south-west part of the county, in the vicinity of Lough Neagh. He 

 first quotes from a work by Barton,* entitled *' Lectures on the Natural 

 History of Lough JSTeagh, 1757 " : — 



" At a place called Ahaness, which is nearly opposite Ham's Island, 

 and not far from Glenavy Waterfoot, the silicified wood is found in a 

 bed of lignite, which is covered by a stratum of clay. At this locality 

 there is a bank on the shores of the lake twelve feet high, and ninety 

 feet distant from the water. Under the following section was obtained 

 by digging : — " The upper stratum is a bed of red clay, three feet deep ; 

 the second, a bed of blue clay, four feet deep ; the third was a stratum 

 of black wood, four feet in thickness, which reposes on another stratum 

 of clay. This stratum of wood is of one uniform mass, and capable of 

 being cut with a spade. Sometimes the wood will not easily break. 

 In that case it requires the aid of some other tool to separate it from 

 the mass, and may, if properly done, afford a block of two, three, or 

 four hundred pounds, which, being carefully examined, is found to 

 consist more or less of stone." To Barton, therefore, the merit is due 

 of being the first to ascertain the relation of the silicified wood to the 

 lignite. 



At Ahaness, Dr. Scouler himself employed a man in digging till he 

 obtained specimens of both kinds of wood. The lignite, he says 

 (p. 236), "consists of portions of stems and branches of trees, but no 

 roots were observed ; but, from the circumstance that many of the 

 specimens still retain their bark, it is probable that they have suffered 

 no lengthened transportation. The wood splits readily in the direction 

 of its fibres ; while in the transverse direction it is broken, so as to 

 display a smooth surface, as if it had been cut by some instrument. 

 This is probably the result of some concretionary arrangement, which 

 has taken place subsequently to the deposition of the wood, and which 

 appears more perfectly in the older and more altered coals of the car- 

 boniferous epoch. This lignite is also sometimes studded over with 

 little crusts s of calcareous matter, which have also penetrated the sub- 

 stance of the wood, forming small veins. This change is probably 

 posterior to the silicifying process, and is perhaps at present in pro- 

 gress. 



"Like the analogous deposit at Verner's Bridge, the depth and 

 extent of the ligniferous bed has not been ascertained, but must be 



* "Journal of the Geological Society of Dublin," vol. i., p. 235. 



