304? ON THE IGNEOUS METAMORPHOSIS [Ch. XIV. 



the sandstone grit which usually accompanies the coal beds, 

 also in a highly indurated state ; its colour changed from red 

 to white, and its mass penetrated by minute grains of iron 

 pyrites. At fifteen yards distance from the dike, the alter- 

 ation ceases, and the sandstone resumes its usual character, 

 becoming reddish and destitute of pyrites. Where the dike 

 traverses the great insulated mass of slate, it is very irregular 

 both in thickness and direction. The works of the Gob col- 

 liery have reached this dike 500 yards inland from the face 

 of the cliff : the coal is altered by it to a considerable distance 

 from its point of contact, being reduced to the state of a 

 cinder, which can be employed only for burning lime. This 

 dike throws out the measures of Gob colliery, which are not 

 recovered on its eastern side : its breadth is about twelve feet 

 where it comes to the surface of the cliff, but varies consider- 

 ably in different parts of its course." * 



" The peninsula of Portrush, which may be about a mile 

 in circumference, is fenced with low cliffs on the west, north, 

 and east ; those on the west present a rude prismatic green- 

 stone ; those on the north and east, tabular masses of green- 

 stone, overlying, and in some places appearing to alternate 

 with a very remarkable rock. It is a flinty slate, exactly 

 similar to the indurated slate-clay which forms the wall of 

 the Carrick Mawr dike, in the Ballycastle collieries ; and the 

 analogy is rendered the more striking from the further resem- 

 blance of the greenstone of that dike to the greenstone of 

 these cliffs. In this flinty slate are contained numerous im- 

 pressions of Cornua ammonis invested with pyrites, the shells 

 being similar to those found in the slate-clay underlying the 

 chalk near Ballintoy : and we felt convinced, while examining 

 the spot, that the rock was no other than the slate- clay of the 

 lias formation, in an indurated state." f 



" The chalk is frequently traversed by basaltic dykes, and 

 often undergoes a remarkable alteration near the point of 



* Gcol. Trans., vol. iii. p. 205. f Idem, p. 212. 



