Lower Palceozoic Rocks of the South-East of Ireland. 



621 



Table XXI. 



Quantities ofElemenls to be added to 100 tons of Main Chain Granite, to convert it into Oreenstones of 

 West Aston, No. 1 and No. 2 ; on the hypothesis that the Silica remains unchanged in amount during 

 the metamorphism. 



Silica, .... 

 Alumina, . . . 

 Peroxide of iron. 

 Lime, .... 

 Magnesia, . . . 

 Potash, .... 

 Soda, .... 

 Protoxide of iron, 

 Loss 



Total, 



It is, of course, improbable that nothing but bases could be added to the 

 molten granite, but this supposition will serve to show the striking difference 

 between the greenstone and granite. 



The quantity of lime, magnesia, and iron required to convert the one into 

 the other is especially remarkable, and it is difficult to imagine- from what 

 source these bases can have been derived. . 



On the whole, the relation between the felstones and greenstones, and the 

 origin of the latter, are the desiderata of the physical geology of the igneous 

 rocks of the district ; and we would suggest the two following points of inquiry 

 as being well worthy of the attention of geological observers : — 



1st. The relations, as to relative position, bedding, intrusion, age, &c., of 

 the hornblendic and felspathic traps of Wicklow, Wexford, and Waterford. 



2nd. The chemical composition of the stratified rocks adjoining the out- 

 bursts of granite and greenstone throughout the same area, with a view to the 

 determination of the probable metamorphism of the main chain granite into 

 the isolated granites and greenstones by the admixture of such adjoining 

 rocks. — S. H. 



VOL. xxiir. 4 ji 



