Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/174

 of that town, the mulattoe rests on a slate clay probably of this formation.

The localities already cited range along the south eastern border of the great basaltic and secondary area; the same formation appears also to exist towards the northern boundary. From specimens which we examined in the collection of the Dublin Society, we had reason to believe that this is the case in the neighbourhood of Ballycastle, but we did not ourselves observe this formation in situ in that point. About half way between Ballycastle and Bushmills near Ballintoy, the chalk formation rises sufficiently high to disclose its substrata; a valley opening towards the sea, near White Park, shews that they here consist of the slate clay of the lias formation, with gryphites and ammonites. Farther east the chalk cliffs again emerge from the level of the sea immediately beyond Dunluce Castle, and continue to rise till they are broken of at the commencement of Portrush Strand. As they here exhibit nearly the same thickness which they possess near White Park, We are naturally led to expect the recurrence of similar substrata near this point; and accordingly, in the peninsula of Portrush, a singular rock is seen, divided by interposed masses of greenstone, but containing ammonites and gryphites, and possessing exactly that character which would be assumed by the slate clay before described, if indurated by the action of heat. In the explanatory notes accompanying the sections of the coast a more detailed account of this peninsula will be found.

The cabinet of the Dublin Society contains specimens of lias from the neighbourhood of Magilligan, about eight miles westward from Portrush, and close to the north-west angle of the basaltic area.