L 112 ] 



XI. 



THE VAEIOLITE OF CERYG GWLADYS, ANGLESEY. By 

 GEENVILLE A. J. COLE, F.G.S, Professor of Geology, Royal 

 College of Science, Dublin. (Plate X.) 



[Eead January 21, 1891.] 



The remarkable rock styled Yariolite, tbe Lajns variolatus of 

 older writers/ cannot even yet be regarded as of wide distribution. 

 While the doctors of the sixteenth century imported specimens 

 from the West Indies as a cure for small-pox, collectors of later 

 times have derived their material almost exclusively from the bed 

 of the Durance. References to known European localities, most 

 of them in Piedmont and the Western Alps, will be found in a 

 recent paper^ on the historic area of Mont Greuevre ; and in 1888 

 I was able to write that variolite, a devitrified spherulitic glass of 

 basic character, was as yet unrecognized in Britain.^ 



In that year, however, the rock was recorded from Ceryg (or 

 Careg) Grwiadys in Anglesey by Prof. J. F. Blake, to whose 

 remarkable keenness of observation we are thus indebted for the 

 discovery of a second rock new to our islands.* In the paper 

 quoted below, the variolite is aptly spoken of as a " spherulitic 

 diabase" ; but in the Report presented to the British Association 

 further petrographical details are given,^ and a thin section of the 

 rock is figured.* 



Last summer, with the aid of directions given by Prof. Blake, 

 I visited this locality in Anglesey in the company of Mr. L. W. 



1 See Aldrovandus, " Musaeum Metallicum" (1648), p. 883. 



2 Cole and Gregory — " The Variolitic Eocks of Mont Genevre," Quart. Journ. Geo!. 

 See., vol. xlvi. (1890), p. 295. 



3 " On Some Additional Occurrences of Tachylyte," Quart. Journ. Geol. Soc, vol. 

 xliv., p. 306. 



* " On the Monian System of Eocks," Quart. Journ. Geol. Soc, vol. xliv., p. 510. 

 ^ "Eeport of the Comm. to investigate the Older Eocks of Anglesey," Erit. Assoc. 

 Eeport for 1888, p. 44 of the separate Eeport. 

 6 Ibid., PI. v., fig. 22, 



