Lower Palceozoic Rocks of the South-East of Ireland. 



619 



larly soda, is very great, and that of silica is small, as compared with the palieo- 

 zoic felspathic traps of the counties of Wicklow, Wexford, and Waterford. 



4. Greenstones associated with the Felstones of the South-East of Ireland. — 

 Although the greater number of the trappean rocks, which occur bedded con- 

 formably with the slates of Wicklow, Wexford, and Waterford, are decidedly 

 felspathic in their character, there are found occasionally other rocks which 

 are genuine greenstones, which occur under precisely similar conditions, and 

 are often intimately connected with the felspathic rocks. In fact, one of the 

 most interesting questions connected with the physical geology of this district 

 is the discovery of the precise relation between the greenstones and felstones 

 which are interstratified with the slates of the Cambro-Silurian age. The data 

 for the solution of this question do not yet exist, and the following analyses 

 of two greenstones from the north-eastern extremity of the trappean bands of 

 rock must be regarded as only a first, and that a small contribution, to our 

 knowledge of this subject. 



The two specimens analyzed occur close to each other near West Aston, 

 county of Wicklow ; and are totally different in physical appearance and cha- 

 racter, though probably similar in their origin. 



Table XX. 



Chemical Composition of West Aston Greenstones. 



Silica, .... 

 Alumina, . . . 

 Peroxide of iron, 

 Lime, .... 

 Magnesia, . . . 

 Potash, . . . 

 Soda, .... 

 Protoxide of iron, 

 Loss by ignition, 



Total 



52-08 

 15-60 

 5-75 

 6-52 

 8-40 

 3-80 

 2-92 

 2-57 

 2-24 



99'88 



57-88 

 15-20 

 7-50 

 4-81 

 6-34 

 3-03 

 2-67 

 1-35 

 1-04 



99-82 



