60 



Fi'occedings of the Royal Irish Acadcmfj. 



less translucent than the preceding zones, and retains clearer traces 

 of organic remains, the pyroxene occurring as an infilling (compare 

 fig. 1). This sequence is seen Tvithin a distance of two centimetres. 



The whole phenomena of Portrush are, of course, on a small scale 

 when compared with those that occur among the roots of mountains, 

 and on the margins of great laccolites and domes. But they corre- 

 spond interestingly with those so well described by Lacroix,^ where 

 fragments of limestone are entombed in basalt near Aubenas, Ardeche. 

 In his figure 8, p. 146, Lacroix shows a zone of augite prisms, 

 embedded in calcite and colourless glass, at the actual contact. The 

 limestone in this case is turned into a yery fine-grained mixture of 

 pyroxene and wollastonite, with some isotropic and some opaque 

 particles. Grains of anorthite occur in the isotropic matter. In his 

 figure 9, p. 148, Lacroix shows veins of basalt in the limestone; 

 vitreous matter is abundant, and the basalt itself, by absorption of 



Section of altered Liassic shale, small quarry, Portrush. Traces of 

 fossil shells remain, infilled and partly replaced by pyroxene. 

 The paler part of the ground is rich in small plates of brown mica, 

 Avhich occur also in the darker and gieyer portion. Minute 

 granules of pyroxene abound throughout, x 15. 



the limestone, becomes more vitreous. Later on,- he describes the 

 marginal zone of silicates formed by the mingling of audesite and 

 limestone on the surfaces of inclusions in the lava of Santorin. 



Fig. 1. 



1 Les Enclaves des roches vulcaniques (1893), p. 144, (fcc 

 - Ibid, p. 264. 



