Page:The Journal of geology (IA journalofgeology21894univers).pdf/74

beds appear to have come from a single one of those subdivisions, one quite above the rocks of Newark, and the same that contains the Richmond coal. That coal, Gilbert says, does not occur in New Jersey, meaning, perhaps, not in large deposits like the Virginian; but yet no doubt it occurs there in thin layers and traces, just as in Pennsylvania, since the same subdivision of rock beds does extend into New Jersey. It is, perhaps, uncertain whether the Newark rocks, with their two reported fossil species, belong even to the Mesozoic.

There is in eastern Pennsylvania and New Jersey great unconformity at the top and bottom of the rocks in question; but it is not yet so certain that beds of the same age as the lowest of them do not occur conformable to Paleozoic beds in western Pennsylvania and elsewhere in eastern America, to say nothing of the West.

Clearly no claim for unity in the supposed group could be based on geographical continuity.

Would it not, indeed, be still more reasonable if he maintained that the Paleozoic rocks of the Appalachian region were a stratigraphic integer or unit, and consequently deserved a separate name?

2. There are, in truth, strong arguments in favor of generally giving local geographical names to stratigraphical groups, whether large or small. Yet there are many names of a different character that have had merit enough to become universally accepted, such as Paleozoic, Mesozoic, the Old and New Red Sandstones, Trias, Oolite, Calciferous, Corniferous, Saliferous, Carboniferous, Coal Measures, Millstone grit, Cretaceous chalk, Eocene and the like. Of course, the larger the group, the less easy to find a suitable, well-characterizing local name, the name of a place or region where the beds have been particularly studied, or much seen of men, or, as a whole, finely displayed; and that would be a difficulty with so extensive a set of beds as the one in question.

3. Gilbert, while insisting that Newark is the proper term in the present case, evidently admits that some such geographical