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Bristol Channel ? between the young redand mulatto along the vale of Geneva ?between mountain limestone and slate inmany parts of Devonshire ? between lime-stone and lias in the district that stretchesfrom Audi to Caliors ? between lias andmulatto at Argenton ? between mountainlimestone and chalk in the Italian Alps ?But will any one affirm that the rocks soblending with each other in external cha-racter are of the same formation ?

So in regard to alternate recurrence. —

Alternating substances are not alwayscoeval; nor do coeval substances alwaysalternate.

The limestones, which near Plymouthalternate with slate, agree with those whichin Cumberland alternate with coal. Arethe slate and coal of the same formation ?

Granite is of one formation; Gneiss ofanother: Do these never alternate, or gra-duate into each other ?