ANNIVEBSAET ADDKESS OP THE PRESIDENT. IxxV 



anorthite, which is unique as to its composition among British 

 rocks *. 



III. The Gh'anites of Donegal, Mayo, and Galway. — These 

 granites are identical in character with those of Scotland, Norway, 

 Sweden, and Finland, and, as such, resemble the granites described 

 by Rose and other chemists. They differ from the granites I. and 

 11. in being stratified and not intrusive, and therefore vary con- 

 siderably in different localities, according to the beds from which 

 they have been formed by metamorphic action. 



Geologically speaking, they may be regarded as belonging to the 

 most ancient of the stratified Scandinavian rocks, and consequently 

 as much older than either the Leinster or Mourne granites. They 

 are not yet proved to be of an age corresponding to the Laurentian 

 rocks of America, although it is very probable that they are so. 



Their mineralogical constituents are : — • 



1. Quartz. 4. Margarodite. 



2. Orthoclase. 5. Lepidomelane. 



3. Oligoclase. 



They are, therefore, quinary granites, and are identical with the 

 granites of Sweden and Norway, from some of which they cannot 

 be distinguished, either by the eye or by the more refined test of 

 chemical analj-sis. 



They differ from the Laurentian stratified granites in not con- 

 taining either labradorite or andesine ; for the existence of such 

 minerals in them has not yet been proved, though often guessed at. 



Labradorite is found in abundance in the stratified granites of 

 Eggeroe, in Norway, and in the gneissose granites of Labrador and 

 Canada, but has not yet been found in Ireland or in Scotland in 

 rocks of the true granite type. 



The celebrated hypersthene and labradorite syenite of Scavig, in 

 Skye, can scarcely be regarded as part of the granitic series of rocks 

 of Scotland. 



In the discussion of the mineralogical composition of the granites 

 of Ireland, Dr. Haughton has adhered to the principle that we are 

 not entitled to assume in any rock the existence of any mineral 

 whose independent existence in that rock has not been proved. By 

 a strict adherence to this principle, he behoves he can confidently 

 state that the results he has obtained, though they may be modified, 

 cannot be refuted by further investigations, and that they will bear 

 the test of time. 



The details of the discussion itself belong to the region of elimina- 

 tion of variables among simple equations, and are familiar to every 

 algebraist, from the time of Bezout to the present day. There is 

 no originality in them, he adds, except such as belongs to the subject 

 to which he has succeeded in applying them. 



It remains to be borne out by further observation whether the 

 above divisions can be relied on in a larger sense ; but from what I 

 have myself seen of the granitic rocks in several of the districts 



* Dr. Haugbton's inrestigations as to the composition and origin of these 

 granites are not yet completed. 



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