By the terms Trap, and Trap-formation, which I am aware are extremely vague, I intend merely to signify a class of rocks, including several members, which differ from each other considerably in mineralogical character, but agree in some of their principal geological relations; and the origin of which very numerous phenomena concur in referring to some modification of volcanic agency.

The probability of our belief in the regularity of natural phenomena increases, indeed, with every new verification of the assumptions based thereon; but, as has been shown, it never rises to absolute certainty.