274

afforded by quartz, amid beds of primitive-slate.

The transition and flotz rocks, which,according to a writer in the Transactionsof the Royal Society of Edinburgh, arenever conformable to each other, are, never-theless, so strictly conformable along thefrontier of Wales , at least to my eyes,that, after repeated examination, I am stillunable to determine where the one form-ation ends, and the other begins.

The planes of mountain limestone, atIngleton, cover the edges of greywackeslate, though, at Orton, these two rocksare conformable, and graduate into oneanother.

In some situations unconformity of pos-ture, far from proving that the strata, inwhich it is observed, were formed at dif-ferent aeras, tends rather to prove thatthese strata were formed simultaneously.It is scarcely possible to imagine how theprimitive limestone of Conemara can havebeen formed at a different period from thatwhich gave birth to the rocks with which