Lower Palceozoic Rocks of the South-East of Ireland. 



607 



constitutes the largest tract of granite iu the British Isles, and also retains 

 throughout its extent the greatest sameness of mineral composition. 



I shall here add, for the purpose of comparison with the foregoing analyses 

 of the Leinster granites, the following analysis of the granite of Creetown in 

 Scotland, which appears to be the prolongation of the Leinster chain, and 

 resembles in its external appearance many of the Leinster granites : — 



Table XI. 



Creetown Granite. 



Granite, medium grained; composed of quartz, white felspar, black mica, with occasional specks 

 of white silvery mica. Not unlike specimens from Dalkey. 



Although this granite looks like the Leinster granites, yet the foregoing 

 analysis is sufficient to prove that it is not the same ; its silica is deficient, and 

 its bases (particularly alumina, lime, and magnesia) are in excess of the 

 average of the Leinster granites. 



II. — Outlying Granitic Tracts. 



1. General Description. — We have already given the geological relations, so 



far as they are known, of the granitic and other igneous rocks which occur in 



the Cambro-Silurian district of the counties of Wicklow and Wexford, and 



mentioned the difiiculty of explaining the absence of the band of felstones and 



greenstones over apart of the northern area, while they stretch so continuously 



across the district on the south. 



4 K 2 



