Page:The Journal of geology (IA journalofgeology21894univers).pdf/73

graphy are (1) definite association of the geographic feature with the terrane, (2) freedom of the term from preoccupation in stratigraphy, (3) priority. The rule of definite association is satisfied if the geographic feature, being a town or district, is wholly or partly underlain by the terrane, or if, being a stream, it crosses the terrane. Preferably the portion of the terrane thus associated should be petrographically and paleontologically characteristic, but this consideration yields to priority.

The "Newark" rocks underlie the City of Newark, exhibiting typical phases of sandstone and shale and containing some fossils. The only other rocks present are of widely different character, being Pleistocene. The name Newark has been applied to no other terrane. It is the earliest geographic name proposed for this terrane.^[1]

Mr. Gilbert has very kindly invited me to answer his argument: (1) that the so-called Newark system ought to have a name, because it is a stratigraphic integer, or unit; (2) that a stratigraphic name ought to include a local geographic term; and (3) that the name Newark is the proper one, because of (a) the definite association of that geographical feature with the rock beds in question, (b) the freedom of the term from preoccupation in stratigraphy, and (c) its priority.

1. He considers that the stratigraphic unit is peculiarly definite from the conspicuous unconformities at top and bottom, while internally it is conformable throughout with little varied composition.

In eastern Pennsylvania, where the rock beds have been studied with some small approach to thoroughness, the composition is found sufficiently varied to justify at least five very conspicuously marked subdivisions of several thousand feet each. Almost all the fossils hitherto used for inferring the age of the