Some Igneous Rocks in Down and Antrim. 53 



other, and thirty yards further south, it was also traversed by a 

 conspicuous greenish granite band about five feet wide. A 

 microscopic section of the more southern basic dyke shows 

 it to be a true basalt. Newer than the granite which it 

 penetrates, it probably represents the Tertiary "Upper Basalts." 

 The greenish granite is a handsome rock, with fairly large 

 crystals of quartz and felspar, coarser in texture than the 

 normal granite, but the difference microscopically is not very 

 great. 



The next slides show dykes on the sea coast, and in connec- 

 tion with these, I may refer to Major Patrickson's paper read 

 before the Geological Society of Dublin in 1835, entitled, "A 

 descriptive list of the dykes appearing on the shore which 

 skirts the Mourne Mountains." His list includes 76 dykes. 

 One of these, No. 48, he mentions as a porphyritic dyke, 

 a quarter of a mile North of Mullartown, and describes Nos. 47 

 and 49 as hornblende dykes in parallel contact with it. These 

 have been identified by Professor Cole with the now well known 

 composite dyke at Glasdrumman Port, minutely described by 

 him in a paper " On derived crystals in the Basaltic Andesite of 

 Glasdrumman Port," * in which he shows that " crystals may be 

 floated away into a pre-existing rock of a low degree of 

 fusibility from one of a higher degree which has intruded into 

 it." The igneous contact described by Professor Cole is 

 illustrated by the next two lantern slides, from Mr. Welch's 

 series of " Irish Geological Views." Hand specimens from this 

 interesting dyke are on the table. 



Passing on to Dunmore Head it may be of interest to note 

 that this is one of the few localities in the British Islands where 

 variolite has been found, and with specimens of the Dunmore 

 variolite, there are others from Annalong, Anglesey, and 

 Australia, the latter particularly interesting as being the first 

 variolite discovered there. It was found in the bed of the 

 Saltwater River, near Sydenham, upon an excursion, conducted 



* Trans. Roy. Dublin Soc. Vol. V., Ser. II., Aug. 1894. 



