512 Scientific Proceedings, Royal Dublin Society. 



variolite in Anglesey^ in 1888 having been regarded as the first 

 occurrence recorded from the British Isles. 



Through the kindness of Sir Archibald Greikie, F.R.S,, I have- 

 been able to examine the type-specimen from the Museum, and also 

 a section which has been prepared from it. In November of last 

 year, with the advantage of the company of Mr. 0. Gr. F. Chute, 

 B.A., I examined the dykes north-east of Kilkeel as far as 

 Glasdrumman Port. 



We found at length, five and a half miles from Kilkeel, a 

 remarkable mass agreeing well with the characters of the specimen 

 in the Museum. On the Ordnance Survey six-inch map, Co. 

 Down, sheet 56, a cottage is shown on the coast 900 feet north o£ 

 the mouth of the Annalong river. Opposite this cottage a group 

 of dykes may be found at low water, having a general south-easterly 

 trend, and perpendicular to the strike of the altered shales and 

 sandstones. It is possible that boulders may have been heaped 

 upon these at the time that the officers of the Greological Survey 

 visited the spot ; for the structure of the variolite is so remarkable 

 among a host of ordinary basalts as to have merited notice in the 

 published memoirs.^ The local absence of dykes on the higher 

 part of the shore may also deceive observers in unfavourable con- 

 ditions of the tide. 



The variolitic dyke appears nearest the land as an elliptical 

 mass some 3 "5 metres long, its longer axis approximating towards 

 the strike of the strata, which have become compressed against it on 

 its east side through movement subsequent to the intrusion. A 

 small rock-pool divides this portion from the next, which runs 

 mainly SE. for 5*2 metres, with a width of 1'2 metres (about 4 

 feet). The dyke then ends abruptly, and reappears 60 cm. to the 

 south, this lateral displacement probably representing a small fault 

 in the strike of the surrounding strata. This third mass runs in 

 the same general direction out to sea, curving at one or two points, 

 and measuring 17 metres. The total length of the masses observed 

 is thus more than 25 metres (82 feet), and the material is pure 

 variolite from end to end. 



1 J. r. Blake, " Eeport of Comm. to investigate Rocks of Anglesey," Brit. Assoc. 

 Report for 1888, PI. v. fig. 22. G. A. J. Cole, Proc. Roy. Dublin Soc, vol. vii. 

 (N.S.), p. 112. 



■>' Explanatory Memoir to Sheets 60, 61, and 71 (1881). 



