[ ] 



VI. 



ON coj^tact-phenomena at the junction of 



LIAS AND DOLEEITE AT POETRUSH. 



By GEENVILLE A. J. COLE, M.E.I. A., F.G.S., 

 Professor of Geology in tlie Eoyal College of Science for Ireland. 



(Plate II.) 



Read November 12. Ordered for Publication November 14. 

 Published December 20, 1906. 



The invasion of the fossiliferous Liassic shales at Portrush, in the 

 County of Antrim, by a basaltic magma of early Cainozoic age, has given 

 rise to features which are famous in the history of geology. Little 

 need now be written on the general physical characters of the 

 junction ; but some details have awaited elucidation, and for these, 

 so far as I am aware, the aid of the microscope has not hitherto been 

 called in. Two circumstances attracted me especially to the Portrush 

 rocks. One was the occurrence, in the collections of the Eoyal College 

 of Science for Ireland, of the original mineral specimens described by 

 Oldham and Portlock^ some seventy years ago. The second was 

 the discovery by the late Mr. A. V. Jennings,^ in 1897, of green 

 soda-pyroxene in a vein associated with the dolerite. During the 

 past five years I have visited the sections at Portrush from time to 

 time, and have gathered the material for microscopic examination 

 which is utilised in the present paper. 



James Bryce, jun.,^ in a paper which made its mark, but which 

 remains none too clear in its conclusions, drew attention to the 

 repetition of the two rock-types, the flinty fossiliferous material 



1 Report on the Geology of the County of Londonderry, &c.. Board o 

 Ordnance (1843), pp. 99, 150, and 742. 



- Irish Naturalist, vol. viii. (1899), p. 64. 



3 An Account of the celebrated Portrush Rock," Journ. Geol. Soc. Dublin 

 vol. i. (1835), pp. 169 and 173. 



