postvolcanic

— In view of the above considerations, it seems reasonable, in endeavoring to find a line of demarcation, as indicated by fossil remains, somewhere in the gravel and volcanic series, to inquire what is positively known to have been found in strata lying undisturbed under the basalt; or, at least, so far down in the volcanic formations as to preclude any possibility that the object in question could have found its way down from a superficial deposit of postvolcanic age.