Sentence:  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 <WSD>neptunians</WSD>; those who have made their observations in the south of the same regions, are generally vulcanists. 
Meaning of the word marked with <WSD> tags:  A proponent of Neptunism.