1908-1909.] 



35 



IRISH HILL. 



The Geological Section of the Club held an excursion to the 

 bauxite mines at Irish Hill, Straid, on the afternoon of 6th June. 

 A party often members travelled by the 1-30 p.m. train to Bally- 

 clare, where they were met by a local member, Mr. Jas. Strachan, 

 under whose direction the visit to the mines was paid. On arrival 

 at Straid Hill House the geologists were welcomed by the Mining 

 Company's Manager, Mr. Furniss, who very courteously conducted 

 them over the principal workings. A few of the members, lamps 

 in hand, accompanied Mr. Furniss into two of the most important 

 of these, where the geological nature of the beds concerned were 

 studied in sitn, and the operations of the miner noted. 



It may be remarked that the interbasaltic beds at Irish Hill 

 are fine examples of the deposits which were formed from the 

 weathering of basalt and rhyolite during the long period of 

 volcanic inactivity between the eruption of the lower and upper 

 basalts. The upper basalt at Irish Hill is almost 150 feet in 

 thickness, and consists of three distinct flows, the two uppermost 

 flows being compact, and the other typically amygdaloidal. 

 Between the upper basalt and the lower is a typical group of 

 interbasaltic beds, including lithomarge, pisolitic iron ore, alumi- 

 nous iron ore, bauxite, and lignite. The lithomarge is over 40 feet 

 thick, and the other beds, varying in thickness from 15 inches to 

 6 feet, overlie the former. The pisolitic iron ore passes gradually 

 into aluminous iron ore, and the latter gradually into bauxite, with 

 which is associated the lignite, both as underlying strata, and 

 included lenticular beds. The iron ore represents the ultimate 

 product of the weathering of the basalt ; and the bauxite probably 

 represents in a similar fashion the final result of the weathering of 

 the rhyolite. The bauxite contains rolled quartz crystals in pro- 

 fusion, and these crystals are identical with the quartz of the 

 rhyolite. The interbasaltic beds are, according to Sir A. Geikie, 

 lacustrine deposits, and there is no doubt that the sedimentary 



