. . .A or overlying group C in that area after prolonged search, we [42] may confidently speak of the fossil as characteristic of the strata B in that area, though without further work, the value of the fossil as a clue to age in other areas would be unproved. It may nevertheless happen, that after more prolonged search in A or C, in the original area a few specimens of the fossil which has been spoken of as characteristic of B may be found in one or other of them, in small quantity. The value of the fossil as one characteristic of B will be slightly diminished, though only slightly, as it is not likely to turn up in numbers in the strata A or C after the prolonged search. Should the fossil be found also to be characteristic of the strata B in areas other than the original one, it becomes of more than local value, and if, after much study it is found to characterise the same strata over wide areas, the cumulative evidence now obtained will render the fossil peculiarly imp. . . Read More