TRANSACTIONS OF SECTION C. 685 



5. On the Occurrence of lolite in the Granite of County Duhlin} 

 By J. Jolt, 1/.^., B.E. 



lolite, not previously noticed in Irish granite, has been found hy the author in 

 the granite of Glencullen. It occurs as a microscopical but abundant inclusion 

 in a substance of felspathic nature which is to be found interpenetrating prisms of 

 beryl. Its presence is confined, apparently, to the felspar so intermixed with beryl. 

 The iolite is in twelve-sided basal prisms, showing the faces /, i-l, i'-S, i-\, O, in 

 size up to O'l mm. in length, transparent, colourless viewed singly, and presenting 

 a vivid and beautiful object in the polarising microscope. Characteristic features 

 are the basal angles of 150°, 120° or 60°; its generally symmetrical extinction on 

 elongated rectangular sections and the transverse cleavafre on such sections. A 

 foliation or plating on 0, and an oblique twming line parallel to I, are also fre- 

 quently met with. Occasionally the crystals occur in radiating groups. Enclosures 

 are rare, generally glass. 



6. An Igneous Succession in Shropshire. 

 By W. W. Watts, M.A., F.G.S. 



The author described the succession of Igneous Kocks in the Shelve aijd Corndon 

 district in Shropshire. 



1. There is a series of Andesitic ashes, interbedded at two principal horizons in 

 the Ordovician sequence. These have a percentage of silica varying from 66-60. 



2. Then come three sets of intrusive masses, a. Andesites (59-54 per cent, of 

 silica). These are intruded into Ordovician rocks, and never touch the Silurian 

 of the district. 6. Dolerites (51-48 per cent, of silica) which are post-Silurian in 

 date. c. Picrites (41-34 per cent, of silica) of later date. These are undoubtedly 

 rocks intermediate in age and composition, but it is difficult to be quite sure of this 

 where the differences in composition are so slight. One, however — the dolerite of 

 Llanfawr — is a very basic dolerite, coming between the normal dolerites and picrites. 

 In minerals a similar transition is to be noted. The Andesites are rich in 

 Hypersthene, the Dolerites rather richer in Augite, while Olivine and Brown INIica 

 come in in the Picrites. The author believed, though he had no means of certainly 

 proving it, that the felspars became more basic in the more basic rocks, but 

 certainly there were different felspars in some of the different members of the series. 

 Another curious point was that the mineral aggregates in glomeroporphyritic 

 Andesites are practically pieces of the ophitic dolerites. The determination of the 

 specific gravities of these rocks gave a similar sequence, the least dense rocks 

 having been erupted first and the denser last. Each of the eruptive rocks occurred 

 in laccolites along the main anticlinal line of the district and also in dykes and 

 along fault lines. 



7. Fourteenth Meport on the Circulation of Underground Waters. 



See Reports, p. 145. 



A List of Works referring to British Mineral and Thermal Waters. 

 By W. H. Dalton. — See Appendix, p. 859. 



Proc. Royal Dublin Soc. vol. v. p. 65. 



