Cole — Contact-Phenomena at Junction of Lias and Dolerite. 63 



invading magma becoming drained out, as it were, into that magma. 

 In view of the small amount of fusion that has taken place in the 

 invaded rock, the local accumulation cannot well be due to a 

 movement of crystallising material through the calcareous shale 

 towards its margin, as has been argued in the case of lava-basins. 

 The possibility of zoning by selective absorption is supported by a 

 contact of granite and garnet-amphibolite at Castleore near Lough 

 Gill. Here a zone consisting wholly of red garnet appears in one 

 place along the junction. The garnet is like that prevalent in the 

 amphibolite ; this latter garnet, moreover, remains in the body of the 

 granite after the other constituents of the complex amphibolite have 

 become absorbed.^ Lacroix,- in one of his examples from Ardeche, 

 regards a zone consisting entirely of pyroxene as a marginal modihca- 

 tion of the invading basalt. In the cases from Portrugh, such zones, 

 however, appear to belong partly to the calcareous shale. 



Below the junction with the Lias, the invading olivine-basalt 

 shades downwards into olivine -dolerite. The latter, as has been 

 often noted, is cut by numerous subsequent veins of dolerite. Olivine 

 is by no means so common in these ; they are also usually coarser in 

 grain and paler in colour than the main mass. Zeolites have arisen 

 in these veins through alteration of the felspar,^ just as is the case 

 in the still more conspicuous veins at Fair Head. The veins often 

 run horizontally along planes of yielding in the main dolerite ; then 

 they bend sharply up or down, and proceed again along another 

 horizontal plane. These horizontal veins or sheets are at times 

 faulted by still later veins. There is no reason to assign any 

 appreciable difference in age to these igneous inflows ; the veins 

 were, however, clearly influenced by planes of weakness, due to 

 shrinkage, in a mass that was practically consolidated. Where they 

 enter the compacter and basaltic layer, they include^fragments of it, 

 just as a granite may include lumps of slate. Though they doubtless 

 represent the upwelling of the last remaining portion of the magma 

 that underlay Portrush, they are subsequent intrusive bodies, and 

 not segregation- veins " in the old and, I venture to think, somewhat 

 fanciful acceptance of the term. The vertical veins terminate 



^ Other details of absorption in Castleore are given in Cole, " Intrusive Gneiss 

 of Tirerrill and Drumahair," Proc. R. Irish Acad., vol. xxiv., sect. B (1903), 

 p. 364. 



^ Les Enclaves des roches volcaniques, p. 148. 



^ Cf. R. B. Young, "An Analcite Diabase and other rocks from Gullane Hill," 

 Trans. Edin. Geol. Soc, vol. viii. (1903), p. 331. 



K.I. A. PROC, VOL. XXVI., SEC. B.] / 



