54- Miss M. K. Andrews on 



in April, 1902, by Dr. Gregory. For this specimen I am 

 indebted to Mr. Chapman, Palaeontologist of the National 

 Museum, Melbourne. 



The next slide shows the position of a large porphyrite 

 (altered andesite) dyke, about a quarter of a mile south of 

 Green Harbour, apparently No. 23 of Major Patrickson's list. 

 In the main central part of the dyke there are very numerous 

 and large crystals of labradorite, and in microscopic section, the 

 schillerization of the labradorite, and the " strain shadows " 

 have a very beautiful effect. 



In the little creek, called ''Goat's Cove," shown in the next 

 slide, there is a small composite dyke I have not seen noted 

 elsewhere. The quartz-porphyry in the centre has an average 

 width of three feet, and is bounded on both sides by a basic dyke 

 into which the acid rock has probably intruded. A few dark 

 inclusions are found in the quartz-porphyry, which in micro- 

 scopic section appear to be altered shale. The position of this 

 creek is a little south of Bloody Bridge, almost immediately 

 below the interesting old ruin of Ballaghanery church, 

 popularly known as St. Mary's. Another composite dyke 

 occurs at Dullisk Cove, just north of this creek. 



The next two views show parts of a very interesting dyke on 

 the sea coast, a little north of Bloody Brrdge, in front of a low 

 hill known as Rock-a-bill. It traverses Silurian strata in a 

 north and south direction, and at the northern end, consider- 

 able patches of the Silurian beds are seen at the surface. The 

 rock appeared at first sight to be a typical quartz-felsite, but 

 microscopic examination of the first slide made, revealed certain 

 characteristics of rhyolites, which indicate the intermediate 

 position it holds between these well marked types. Dr. Cnllis, 

 to whom it was shown, described it as a " stony rhyolite 

 approaching quartz-felsite." * Other microscopic sections show 

 the base in various stages of devitrification. This dyke cuts 



* Mr. H. J. Seymour asked for the loan of this microscopic section to exhibit before 

 the Dublin Microscopical Club, and the details he then gave are published in " The 

 Irish Naturalist," Sept., 1897, p. 2+8 



