Yol. 54.] LIMESTONE OF THE COUNTRY AROUND LLINDCJDNO. 399 



& Mode of Occurrence of the Dolomitic Eocks of Kilkenny,' by 

 Mr. Andrew Wyley/ in which he described the alteration of parts 

 of the Carboniferous Limestone into dolomite in a very capricious 

 manner along the beds, and sometimes enclosing large masses of 

 unaltered limestone, the change being always exceedingly abrapt. 

 He described dykes of dolomite between joints, where it has lost all 

 traces of the original stratification, and others where the bedding 

 can be traced across from the limestone on each side. Mr. Wyley 

 was of opinion that the metamorphism was produced by the passage 

 upwards from great depths of water containing magnesium car- 

 bonate ; that the alteration took place after the deposition of the 

 Permian Limestone, and that both formations were dolomitized by 

 the same upflow of magnesia, and at the same time. 



If I was correct, in my paper on ' The Carboniferous Limestone 

 of the Yale of Clwyd,' ^ in assigning the faulting of that formation 

 in jSTorth Wales to the end of the Triassic, the metamorphism may 

 have been produced in the Jurassic Period. In Kilkenny the 

 alteration extends over a considerable area, but around Llandudno 

 the dolomite may be seen presenting the most interesting variations 

 within an area of a few square miles, and it is remarkable that it 

 has not been described before. 



In Kilkenny there are beds of limestone containing from 3 to 6 

 per cent, of magnesium carbonate, but around Llandudno the 

 limestone contains only a mere trace of it. No dolomite occurs in 

 the Yale of Clwyd, but in the Upper Grey Limestone at Penmon 

 (Anglesey) there is a bed 30 feet in thickness. 



Discussion. 



Dr. SoRBT said that, being convinced that in many cases dolomite 

 had been formed by the replacement of half the carbonate of lime 

 in limestones by carbonate of magnesia, he had been anxious to 

 produce this change artificially, but so far had not succeeded. He 

 had been able, at a fairly high temperature, to replace entirely the 

 carbonate of lime ; but not merely one half so as to form true 

 dolomite. Sundry experiments, which have now been going on for 

 36 years, show that in some cases such long- continued action will 

 produce changes which a few years fail to produce ; and perhaps 

 the formation of true dolomite depends on a very long-continued 

 action at the ordinary temperature. 



Dr. Hicks said that the Society was to be congratulated on 

 receiving this further evidence of careful and original work from 

 one who had been for so many years an active Fellow of the Society. 

 No one had done so much as the Author, in North Wales, in 

 working out the fossil-zones in the Carboniferous rocks, and the new 

 fact now brought forward that the ' Lower Brown Limestone ' has, 



1 JouTB.Geol. Soc. Dublin, vol. vi (1854) p. 109. 

 =^ Proe. L'pcol Geol. Soc. vol. viii (1897-98) p. 32. 



Q. J. G. S. No. 215. 2 p 



