410 Scientific Proceedings, Royal Dublin Society. 



Iron-pyrites and ilmenite are present: the latter is mostly 

 altered into granular aggregates of sphene. The amount of 

 chlorite and quartz is naturally in direct proportion to the degree 

 of alteration the rock has undergone. The chlorite is to he re- 

 garded as the final product of the alteration of the hornblende. 

 A quantity of iron and lime, liberated by this chloritisation, led 

 also to the formation of epidote and zoisite. Apatite is rare. 

 There is no trace of either scapolite or sahlite in the specimens 

 examined. It is, however, highly probable that both these mine- 

 rals are to be met with in the greenstones of this district, as Sir 

 Charles Giesecke records their occurrence at the old lead mine in 

 the vicinity of Strabane, Co. Tyrone. 1 The scapolite shows a 

 " four-sided prism ; " whilst the sahlite is described under the old 

 name " baikalite." The same mineralogist calls attention to the 

 presence of a " silver-white, pearly mica, resembling lepidolite," 

 at Hollyhill, Co. Tyrone, where he also observed lievrite. 



1 l. c. pp. 208, 219. 



