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VIII.— NOTES ON THE MINERALS OF THE DUBLIN AND 

 WICKLOW GRANITE. I.— THE BERYL AND IOLITE 

 OF GLENCULLEN. By J. JOLY, B.E., Assistant to the 

 Professor of Engineering, Trinity College, Dublin. (With 

 Plates II., III., and IV.) 



[Eead, November 18, 1885.] 



The beryls described in the following pages occur in the granite 

 exposed in the quarries of Grlencullen, Co. Dublin, close over the 

 little stream, Cookstown Eiver, which flows into the village of 

 Enniskerry, some three miles further on. These quarries are 

 situated about one mile from the junction of the granite with the 

 schist. Other and larger quarries opened higher up on the same 

 side of the valley yielded, on examination, only one small specimen. 

 In the lower quarries these beryls occur in abundance — an abun- 

 dance equalled by no other locality in the Dublin and Wicklow 

 granite, so far as I know. 



I can find no previous mention of this locality anywhere in 

 published records. 1 In Weaver's remarkable and beautiful work 

 on the geology of Eastern Ireland 2 the locality is unmentioned. 

 Weaver was the first to find beryls in the granite. It is strange 

 that the Grlencullen beryls escaped notice so long. The quarries 

 are very old, and beryls have occurred in them, I am informed by 

 the quarrymen, from the first. 



The crystals, which are sufficiently remarkable in habit and 

 structure to justify close investigation, occur in veins and bunches 

 throughout the granite, generally coarsely crystallized in their 

 immediate neighbourhood. Orthoclase, especially, occurs in re- 



1 Prof. J. P. O'Reilly's visit (Proc, R. D. S., vol. iv., p. 505) was made some 

 months after mine, which took place in January, 1885. 



2 " Memoir on the Geological Relations of the East of Ireland," by T. Weaver. 

 From vol. v. of the Transactions of the Geological Society of Ireland, 1819. This 

 work is too much neglected : the engravings of mountain profile are exquisite ; the 

 letterpress, with all the freshness of " the Complete Augler," is a record of patient and 

 conscientious research. 



