CHAPTER III.
Lamarck's Theory of Progression illustrated.—Class of Facts which give Color to it.—The Credulity of Unbelief.—M. Maillet and his Fish-birds.—Gradation not Progress.—Geological Argument.—The Present incomplete without the Past.—Intermediate Links of Creation.—Organisms of the Lower Old Red Sandstone.—The Pterichthys.—Its first Discovery.—Mr. Murchison's Decision regarding it.—Confirmed by that of Agassiz.—Description.—The several Varieties of the Fossil yet discovered.—Evidence of violent Death in the Attitudes in which they are found.—The Coccosteus of the Lower Old Red.—Description.—Gradations from Crustacea to Fishes.—Habits of the Coccosteus.—Scarcely any Conception too extravagant for Nature to realize,
CHAPTER IV.
The Elfin-fish of Gawin Douglas.—The Fish of the Old Red Sandstone scarcely less curious.—Place which they occupied indicated in the present Creation by a mere Gap.—Fish divided into two great Series, the Osseous and Cartilaginous.—Their distinctive Peculiarities.—Geological Illustration of Dr. Johnson's shrewd Objection to the Theory of Soame Jenyns.—Proofs of the intermediate Character of the Ichthyolites of the Old lied Sandstone.—Appearances which first led the Writer to deem it intermediate.—Confirmation by Agassiz.—The Osteolepis.—Order to which, this Ichthyolite belonged.—Description.—Dipterus.—Diplopierus.—Cheirolepis.—Glyptolepis,
CHAPTER V.
The Classifying Principle and its Uses.—Three Groups of Ichthyolites among the Organisms of the Lower Old Red Sandstone.—Peculiarities of the Third Group.—Its Varieties.—Description of the Cheiracanthus.—Of two unnamed Fossils of the same Order.—Microscopic Beauty of these ancient Fish.—Various Styles of Ornament which obtain among them.—The Molluscs of the Formation.—Remarkable chiefly for the Union of modern with ancient Forms which they exhibit.—Its Vegetables.—Importance and Interest of the Record which it furnishes,