the jaw, found in the sandstone cliffs that overhang the Findhorn, measures an inch in diameter at the base. A second tooth of the same formation, of a still larger size, disinterred by Mr. Patrick Duff from out the conglomerates of the _Scat-Craig_, near Elgin, and now in his possession, measures two inches in length by rather more than an inch in diameter. (See Plate X., fig. 4.) There occasionally turn up in the sandstones of Perthshire ichthyodorulites that in bulk and appearance resemble the teeth of a harrow rounded at the edges by a few months' wear, and which must have been attached to fins not inferior in general bulk to the dorsal fin of an ordinary-sized porpoise. In short, the remains of a Patagonian burying-ground would scarcely contrast more strongly with the remains of that battle-field described by Addison, in which the pygmies were annihilated by the cranes, than the organisms of the upper formation of the Old Red Sandstone contrast with those of the lower.[AO] [Footnote AO: 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.] [Illustration: _PLATE X._]