﻿Vol. 64.] EOCKS OF GLENDALOUGH AND GRETSTONES. 487 



Besides these colourless minerals of the epidote-group, a brown 

 allanite occurs in small quantity, with the usual outgrowth of 

 clinozoisite. It has determined a pleochroic halo in the surrounding 

 actinolite. Most of the pleochroic halos are found, however, round 

 minute colourless grains which sometimes resemble apatite. These 

 are mostly clinozoisite, but occasionally a core of allanite may be 

 detected. 



Fig. 6. — The ' miocecl rock^ Glendalougli ; clinozoisite and actinolite 

 lying in a matrix of quartz and felsj)ar. (Magnified SO diameters.) 



The garnet shows thoroughly idiomorphic outlines, and includes 

 apatite, clinozoisite, biotite, and actinolite. The last two may, 

 however, have penetrated along its cracks. There is no evidence 

 to show that its presence is due to absorption of the schists, as 

 Prof. Cole has suggested.^ 



The hornblende presents generally an actinolitic habit, and 

 is green in colour. Even the large-bladed types are resolved in 

 sections into numerous parallel fibres, while a sheaf-like splitting 

 at the ends is universal. Elegant radial clusters of actinolite are 

 common, and isolated fibres are found in the felspar, quartz, and 

 garnet. An important exception to this habit occurs in a few large 

 plates, which consist outside of fibrous actinolite as usual, but 

 contain in their centre irregular remnants of brown hornblende 

 with the peculiar striations already described. It is the same as 



^ Proc. Eoy. Irish Acad. vol. xxv (1905) sect. B, p. 119. 



