312 Scientific Proceedings, Jioyal Dublin Society. 



litliomarge, it leached the iron out of it, and left a residuum of 

 alum clay ; consequently the upper portions of the beds are richest, 

 ■while in depth they graduate into lithomarge. At first lithomarge, 

 alumite, and lignite gradually filled up the lakes ; next, these ac- 

 cumulations were covered over by a flow or flows of dolerite, the 

 steatitic rocks (Nos. 5 and 6) being the tuffose and decomposed 

 underneath portion of the flow. 



Nos. 3 and 4, Bole or Alumnious Iron Ore (2nd ore), and the 

 Pisolitic or Pebbly Ore (1st ore). — We have next to consider how 

 these ores accumulated between the lithomarge- and dolerite. It 

 would appear evident that they are younger than the overlying 

 bed of dolerite, for the following reasons : first, coming up through 

 ihe iron ore measures in the Glenariif mines, as mentioned by Mr. 

 P. H. Argall,^ there are nearly perpendicular dykes bearing about 

 N. 16° W. These are thus described : — " These dykes may be 

 divided into two distinct classes: first, those which stop at the roof, 

 or stop dykes, and second, those that penetrate the roof, or through 

 dykes; the latter invariably displace the ore measures, and bake the 

 pisolitic seam, while the " stop dykes" neither displace nor bake the 

 seam. The dykes that stop at the roof have a steatitic parting 

 separating them from it, similar to that above the pisolitic ore." 



Some of the " stop dykes" turn over or " splash" against the 

 roof, which goes to prove that they are newer than it ; while the 

 " through dykes" in general can be traced up to the sheet of dolerite 

 to which they belong. " As already stated, the pisolitic ore is neither 

 baked nor displaced by the majority of the dykes which stop at the 

 roof ; while it is nearly always displaced and indurated by the dykes 

 which penetrate the roof ; from which it would appear that the 

 pisolitic ore was formed prior to the latter and subsequent to the 

 former." 



The pisolitic ore has larger pisolites and is richer at the surface, 

 the richness and size of the pisolites decreasing downward gradually, 

 till it merges into the bole, which often is too poor to be profitably 

 worked. The ore seam (Nos. 3 and 4) is of very irregular thickness, 

 as in some places the roof descends until it rests on the " pavement," 



1 Scient. Proc. E.D.S., vol. iii., new series. Mr. Argall, late resident agent of the 

 Glenariff mines, has examined the iron ore measures very carefully, and from his notes 

 we will q^uote frequently. 



