W. H. Westropp — Albite in Leinster Granite. 561 



M. G. S. Memoirs of the Geological Survey of Great Britain. 



P. G. S. Proceedings of the Geological Society of London. 



J. G. S. Journal of the Geological Society of London. 



Rep. Brit. Ass. Report of the British Association for the Advancement of 

 Science. 



King Perm. Foss. Palseontographical Society, Monograph of the Permian Fos- 

 sils of England, by William King. 



Pesch. Lab. Monographia dei Pharyngodopilidae Studi Palseontologici del 

 Del. Cav. Prof Igino Cocchi, 1864. 



Dixon, F. S. Fossils of the Tertiary and Cretaceous formations of Sussex, by 

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Phil. Trans. Philosophical Transactions of the Royal Society. 



Geol. Mag. Geological Magazine. 



VII. — On the Occukrenoe op Albite in the Granite of Leinster. 

 By "W. H. Stacpoole "Westropp, M.R.I.A. 



DURING the past summer, I had the good fortune to detect Albite 

 (Soda-feldspar) in some blocks of granite in the wall of the west 

 pier at Kingstown, Co. Dublin. As the pier is built of rock from 

 the Dalkey quarries, the mineral can be referred, with tolerable cer- 

 tainty, to its original locality. I was induced to look closely at the 

 above-mentioned blocks, through noticing that they contained a 

 mineral of a purple colour ; this proved to be fluor, which occurs 

 sparingly throughout the Leinster granite. Associated with the 

 fluor was a pretty considerable quantity of a white mineral, occur- 

 ring in aggregations of minute crystals ; this appeared to me to be 

 so like Albite that I considered it deserving a careful examination. 

 I brought some of it to the Eev. Professor Haughton, F.R.S., who 

 agreed with me in thinking that it had a very albitic look, and 

 kindly undertook to have it analyzed, which has been done with the 

 following result :- — 



Silica 64-70 



Alumina 

 Potash .. 

 Soda 

 Loss 



2L80 

 2-84 

 9-78 

 0-30 



99-42 

 Unfortunately the quantity which could be separated sufficiently 

 pure for analytical purposes was very small. 



This discovery is one of no little interest in the correlation of the 

 irruptive granites of Leinster with those of Mourne and Cornwall. 



There can be little doubt but that most, if not all. granite contains 

 a second feldspar in addition to Orthoclase (Potash-feldspar). 



The second feldspar that is a constituent of the bedded granites 

 of Connaught, Donegal, parts of Scotland, and Scandinavia, is always 

 oligoclase. The opinion is daily gaining support that these bedded 

 rocks are really of metamorphic origin. 



Oligoclase has never been found in irruptive (intrusive) granites, 

 such as those of Leinster, Mourne, Cornwall, and parts of Scotland, 

 but it is not improbable that Albite may be a normal constituent, 

 though not always occurring in the crystalline condition. 



It is some years since Professor Haughton, in the first of his well 



VUL. VI. — NO. LXVI, 36 



