Ix PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



under the Chalk of the south-east of England. The further considera- 

 tion of this important question was referred to a Committee, who will, 

 I trust, be able to report on it at some early future Meeting of this 

 Society. In the mean time it is to be hoped that parties will be 

 found with sufficient enterprise and energy to prosecute the search, 

 until either the water-bearing strata shall have been reached, or the 

 nature of this somewhat anomalous formation shall have been 

 ascertained. 



The question of the chemical composition of granite has been 

 carefully studied of late years by Prof. Haughton, and numerous 

 papers on the subject from his pen and that of Prof. Galbraith, have 

 appeared in many of the scientific publications in London, in Dub- 

 lin, and in Edinburgh. His inquiries have hitherto been almost, if 

 not entirely, confined to the granites of Ireland ; and some of the 

 results of his investigations and analyses have been recently brought 

 under our notice in a paper entitled " Experimental Researches on 

 the Granites of Ireland." The first part of the paper described the 

 granites of the south-east of Ireland, which are reducible to three 

 types depending on their chemical and mineralogical composition. 

 The granite of the first type, which Prof. Haughton proposed to call 

 *' potash-granite," is found in the main granitic chain of Wicklow 

 and Wexford, and at Carnsore in the south-east of Ireland. The 

 granite of the second type, which is a '* soda-granite," occurs at 

 Rathdown and Oulast, and is distinguished from the former by a 

 diminution of silica and an increase of lime and soda. The third 

 granite is peculiar, and is found only at Croghan Kinshela, near the 

 gold mines of Wicklow. It consists of quartz, albite, and chlorite, 

 while the potash-granites of the main chain consist of quartz, ortho- 

 clase, and margarodite (mica). The three granitic districts of the 

 north-east of Ireland are then described. They are known as the 

 Mourne, Carlingford, and Newry districts. The granite of Mourne 

 consists of quartz, orthoclase, albite, and a green mica, probably 

 similar to margarodite. The Carlingford granite is a '* potash- 

 granite," in which hornblende replaces mica. At the junction of 

 this granite with the carboniferous limestone, a remarkable change 

 takes place in the granite on penetrating the limestone in dykes. 

 From being originally a compound of quartz, orthoclase, and horn- 

 blende, it is converted by the addition of lime into a compound of 

 quartz, hornblende, and anorthite, which last mineral was noticed for 

 the first time as entering into the composition of British rocks. The 

 Newry granites belong to the " soda-granite " type, and resemble in 

 many respects the secondary granite of the Wicklow and Wexford 

 districts. 



I am not aware that any practical results have yet been obtained 

 from these analyses, and the knowledge of these elementary di- 

 stinctions in the composition of the granites. Perhaps, as the inves- 

 tigations are extended to the granites of other countries, where their 

 conditions may be different, we shall obtain some information as to 

 the different ages of these differently combined rocks. At all 

 events, we are under great obligations to Prof. Haughton for having 



