Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/221

 some places appearing to alternate with, a very remarkable rock which has been the subject of much discussion among the supporters of opposite theories.

It is a flinty slate, exactly similar to the indurated slate clay which forms the wall of the Carrick Mawr dyke, in the Ballycastle collieries; and the analogy is rendered the more striking, from the further resemblance of the greenstone of that dyke to the greenstone of these cliffs. In this flinty slate are contained numerous impressions of cornua ammonis invested with pyrites, the shells being similar to those found in the slate clay underlying the chalk near Ballintoy.

The advocates of the Neptunian theory consider this rock as a variety of basalt, and refer triumphantly to its included fossils, as affording a conclusive argument against the Volcanists.

Professor Playfair, on the other hand, expresses his belief that “ the rock containing the shells is the schistus or stratified stone, which serves as the base of the basaltes, and which has acquired an high degree of induration by the vicinity of the great ignited mass of whinstone.” See illustrations of the Huttonian theory.

The resemblance of this rock to the indurated slate-clay of Carrickmawr, and the identity of its fossils with those of the slate-clay underlying the chalk near Ballintoy, together with the relative position of Portrush and of the chalky cliffs on the east, appeared to us to give the greatest weight to this very ingenious conjecture; 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.

The remaining portion of the section will sufficiently explain itself: it terminates where the secondary formations turning to the south finally quit the coast. The headland of Macgilligan, the most northern point of the mountain range formed by their escarpment