Neptunian

In several important cases, it is difficult to determine to what degree the metamorphosis has extended, since it remains uncertain whether the form and structural remains of the neptunian sedimentary formation, or as a product of the metamorphosis itself; for the original form of the neptunian, as well as of the volcanic sedimentary rocks have often become so changed by erosion, and so much alike in both classes of rocks, that this distinctive character is wholly lost; [...]

As to the two theories, neither will suffice alone. The neptunian is utterly inadequate to explain the phenomena of basalt; nor can a vulcanist account for the appearance of an hydrophane.—We need both explanations. Those geologists who have travelled in the north of Europe, are generally neptunians; those who have made their observations in the south of the same regions, are generally vulcanists.