Sollas — On Soda Granites and Associated Dykes of Wicklow. 265 



I have not yet completed the investigation, occurs sometimes in 

 association with biotite, and most frequently with its green variety, 

 sometimes also as an inclusion in the central parts of the zonal 

 plagioclase felspar, and sometimes in plates filling up the inter- 

 stices between adjacent crystals of felspar. 



A preliminary analysis of 0*0750 gramme gave the follow- 

 ing :— 



Per cent. 



Silica and other oxides (Ti0 3 , &c), 0-0298 3970 



Alumina, ferric oxide, &c, . . . 0-0268 35-00 



Lime, 0-0162 21-60 



Magnesia, 0-0005 0-66 



Water, 0-0012 1-60 



0-0745 98.56 

 Further treatment gave : — 



Per cent. 



Silica, 0-0240 32.00 



Other oxides, associated with silica, 0*0058 7*70 



Alumina, 0-0056 7-46 



G-lucina(P), 0*0031 4-13 



Ferric, and other oxides, .... 0*0140 18*66 



The optic axial plane is situated at right angles to the chief 

 cleavage, the dispersion is inclined, and p is greater than v. 



Biotite. — Sections of this parallel to the basal plane sometimes 

 present a hexagonal outline, but are more frequently quite irregu- 

 larly bounded, and the hexagonal outline, even when present, is 

 usually more or less ragged. Sections more or less normal to the 

 the basal plane are rectangular, sharply bounded laterally by the 

 basal plane, but almost always much eroded at the ends. Inter- 

 laminated with the brown mass of the crystals a green coloured 

 portion occurs. It is usually sharply bounded by the straight 

 cleavage planes, and more often occurs in the interior than towards 

 the exterior of the crystal. Along the cleavage planes of this 

 green part crystals of epidote have been developed ; magnetite also 

 has been extruded. 



Clusters of zircon and apatite crystals, common enough within 

 the biotite, may also be seen lying in the minerals immediately ad- 

 jacent to it, especially where its boundary is most ragged. In 



X2 



