In the last-mentioned locality, in a beautifully wooded dell, known as the Den of Balruddery, the _Cephalaspis_ is found associated with an entire group of other fossils, the recent discovery of Mr. Webster, the proprietor, who, with a zeal through which geological knowledge promises to be materially extended, and at an expense of much labor, has made a collection of all the organisms of the Den yet discovered. These the writer had the pleasure of examining in the company of Mr. Murchison and Dr. Buckland: he was afterwards present when they were examined by Agassiz; and not a single organism of the group could be identified on either occasion, by any member of the party, with those of the lower or upper formations. Even the genera are dissimilar. The fossils of the Lias scarce differ more from those of the Coal Measures, than the fossils of the Middle Old Red Sandstone from the fossils of the formations that rest over and under them. Each formation has its distinct group--a fact so important to the geologist, that he may feel an interest in its further verification through the decision of yet another high authority. The superior Old Red Sandstones of Scotland were first ascertained to be fossiliferous by Professor Fleming, of King's College, Aberdeen,[AM] confessedly one of the first naturalists of the age, and who, to his minute acquaintance with existing forms of being, adds an acquaintance scarcely less minute with those forms of primeval life that no longer exist. He it was who first discovered, in the Upper Old Red Sandstones of Fifeshire, the large scales and plates of that strikingly characteristic ichthyolite of the higher formation, now known as the _Holoptychius_--of which more anon; and, unquestionably, no one acquainted with his writings, or the character of his mind, can doubt that he examined carefully.