356 [Proc. B.N.F.C, 



furnace, but its nature has not been determined. It occurs like- 

 wise in the altered Portrush rock, and is thought to be Hauyn, a 

 volcanic mineral found near the Rhine, in Germany. These are 

 only the most prevalent kinds of minerals; others occur which have 

 not yet been identified. Nowhere in our district can such a variety 

 be found in so small a compass, nor in such abundance as in this 

 old volcanic vent. Hullite also occurs as a thin glaze or film on the 

 joints and fissures of basalt at other localities near Belfast, the 

 Giants' Causeway, and Knocklayde, and has caused the igneous 

 rocks to be mistaken for coal by not only the unlearned, but by 

 " men of science." Although it looks like coal, it contains no 

 carbonaceous matter, and the simple test of putting it into a fire 

 would increase the knowledge of many individuals, and keep them 

 from indulging in useless conjectures. 



Mr. Gault concluded by stating his views regarding the origin 

 of the Hullite and other silicious minerals referred to. Into the 

 volcanic neck of Carnmoney, long after the volcanic forces had 

 spent their vigour, and were fast dying out, alkaline water at a 

 high temperature found access. This would dissolve the silica in 

 the basalts, and form a sort of gelatinous or colloid state of silica 

 that would percolate through the fissures and cavities in the 

 dolerite rocks, and would probably combine with some of the 

 many varieties of iron to form the Hullite and other ferruginous 

 silicates. These fluid combinations would solidify and crystallise. 

 Violent explosions of gaseous matter would take place from time 

 to time, and blow off portions of the walls of the vent. Some of 

 these solid basalt fragments would fall back again into the fissures, 

 and after some time would be enveloped by the layers of silicious 

 matter. Thus often do we find hard masses of dolerite forming 

 a nucleus, around which the opal and chalcedony is gathered in 

 many concentric layers. This process would be continued until 

 the volcanic forces became extinct in Antrim, and moved north- 

 ward to Mull, Staffa, and other Hebridean islands; and finally 



