410 PEOCEEDmes of the geological societt. [June 18, 



XV. Anagarry. — A felspathic paste, with large crystals of orthoclase and frag- 

 ments of quartz : contains also crystals of sphene, locally abundant 

 (and occasional hornblende (?) in :J in. crystals). It is found beside 

 the limestone, whenever the latter comes in contact with the granite, 

 as at Anagarry, Grlenlehen, and Barnesbeg. 



The portion analysed was carefully freed from hornblende and 

 sphene. From the preceding Table, it is evident that the granites 

 of Donegal differ from each other much more in chemical composition 

 than the granites of Leinster already described by me*. This dif- 

 ference was to be expected from the more decidedly eruptive charac- 

 ter of the Leinster granites, wbich nowhere simulate the stratified 

 character so remarkable in those of Donegal. 



The granites Nos. IV. and XIII., for example, are rather to be 

 considered as gneiss than granite ; and their exceptional composi- 

 tion may be accounted for by this circumstance; but, as I have 

 already observed, it is almost impossible to teU where the gneiss ends 

 and the granite begins. 



V. Minerals of the Granite of Donegal. 

 The minerals of the granite of Donegal may be divided into 

 Constituent and Accidental Minerals. 

 The Constituent Minerals (A) are — 



1. Quartz. 



2. Orthoclase. 



3. Oligoclase. 



4. Black Mica. 



5. White Mica (sometimes). 



6. Hornblende (sometimes). 



Of these, the first four are always present, and easily distinguish- 

 able from each other ; the fifth mineral, white mica, is found locally 

 abundant, particularly in veins, associated with special accidental 

 minerals; and the sixth mineral, hornblende, is found intimately 

 mixed with black mica [as in lepidomelane, Soltmann] in the more 

 basic varieties of the granite. 



The Accidental Minerals (B) are — 



1. Sphene. 4. Garnet. 



2. Schorl. 5. Molybdenite. 



3. Beryl. 6. Copper-pyrites. 



A. Constituent Minerals. 



1. Quartz. — The quartz entering into the composition of the 

 granite is of the usual grey variety ; when found in veins, it some- 

 times forms fine black crystals, as at Barnesmore Gap, and some- 

 times smaller crystals of a rose-colour, as at Barnesmore and Shes- 

 kina-roan. 



2. Orthoclase. — The orthoclase of the Donegal granite is generally 

 red, but sometimes white: the following analyses show its com- 

 position : — 



* Quart. Joui'n. Geol. Soc. Lond. Aug. 1856, vol. xii. p. 177. 



