g 4 [Proc. B.N.F.C., 



4. Occasionally, when the glassy material in the Basalt is very 



sparse, or when the layer of this material is brecciated, the first 

 Zeolite deposited — usually Natrolite — contains inclusions of 

 Augite, Plagioclase Felspar, and Magnetite, similar to the 

 primary minerals of the Basalt, but usually much larger. 



5. In such cases, where the Zeolite contains inclusions of primary 

 minerals, a remarkable feature developed in that portion of 

 the Basalt immediately surrounding the Zeolite is its 

 completely holo-crystalline structure, which is frequently even 

 granitic (Fr. grenue). The included crystals are often as much 

 as ten times larger than the crystals of the same mineral in 

 other portions of the rock itself. 



6. When the green glassy layer is brecciated — most probably 

 pseudo-brecciated by the vagaries of crystalline force — the 

 detached portions may be observed in contact with, and 

 often completely coating, the included crystals of Augite, 

 Felspar, and Magnetite. When the glassy material is sparse 

 it may be observed sticking on to the included crystals — 

 chiefly the Felspars — in the form of minute spheres and 

 hemi-spheres. 



7. A common and peculiar structure in many of the Co. Antrim 



Basalts is the aggregation of Magnetites close to the green 

 glassy layer lining the Zeolite cavities. Sometimes a string 

 of small crystals of Magnetite may be observed quite close to 

 the edge of the cavity and investing the latter, not exactly in 

 a layer, but approaching such a structure. 



The occurrence of Natrolite, containing inclusions of primary 

 minerals, in Co. Antrim, yields rather important evidence tending 

 towards the elucidation of certain problems in the geogenesis of 

 so-called " secondary " minerals in lavas. The Zeolite, Analcime, 

 has been proved to exist in such rocks as the Monchiquites and 



