Note AO — Chapter IX

I have permitted this paragraph to remain as originally written, though the comparatively recent discovery of a gigantic Holoptychius (?) in the Lower Old Red Sandstone of Thurso, by Mr. Robert Dick of that place, (see introductory note,) bears shrewdly against its general line of statement. But it will, at least, serve to show how large an amount of negative evidence may be dissipated by a single positive fact, and to inculcate on the geologist the necessity of cautious induction. An individual Holoptychius of Thurso must have been at least thrice the size of the Holoptychius of the Upper Old Red formation, as exhibited in the specimen of Mr. Noble, of St. Madoes.