364 Scientific Proceedings, Royal Dublin Society. 



I should mention that this effect on the magnet would appear 

 to have been observed before, for when I was examining the rock 

 an intelligent old countryman came up and spoke thus — I give 

 his own words, as they are brief and pithy : " That's a mighty 

 quare rock, sir. They do say that it never could be surveyed 

 by mortal man. Them that tried it always found their instru- 

 ments went wrong, and they could make no hand of it at all, at all." 



Chemical Composition. — This is nearly that of most rock 

 serpentines, except that it is highly aluminous even when it is 

 perfectly compact and has no visible traces of tremolite or 

 asbestus, in which alumina might be supposed most likely to 

 occur. Indeed an analysis is not required to prove this point as 

 the compact rock when breathed upon gives the peculiar earthy 

 odour of aluminous rocks ; but the chief points worthy of remark 

 about the rock are the presence of magnetite and of nickel. As 

 to the latter it has not often been found in serpentine. There are 

 a few instances mentioned by Dana. It has been recorded as 

 occurring in the Black Serpentine of the Lizard by Bonney and 

 Huddleston, and I myself have noticed it in that of Croagh 

 Patrick, county Mayo, a rock which closely resembles the Sligo 

 one. It very likely takes the place of some of the magnesium. 

 ' Stromeyer has obtained from 0*22 to ()-45 per cent. Ni O in Ser- 

 pentine of Eoraas, Tundal, and Saxony ; Lynchnell and Sterry 

 Hunt 2*24 per cent., in the serpentine of some parts of America, of 

 Cornwall, of Banffshire, of the Vosges, France. 



I have not had time to make a complete series of analysis 

 of this very interesting rock, but the following will give a fair 

 idea of its general character. 



Compact Serpentine. 



AI3O3, 



Fe,03, 



FeO, 



MnO, 



Ni O, 



Ca O, 



MgO, 



Water, 



Maenetite Fe, O, 



Analysis I. 



No Magnetite apparent on casual 



Ohservcution. 



38-13 

 5-5 

 1-30 

 6-00 

 0-95 

 1-25 

 1-00 

 30-32 

 12-80 



4-0 



99-75 



