CHAPTER IX.

Fossils of the Upper Old Red Sandstone much more imperfectly preserved than those of the Lower.--The Causes obvious.--Difference between the two Groups, which first strikes the Observer, a difference in size.--The _Holoptychius_ a characteristic Ichthyolite of the Formation.--Description of its huge Scales.--Of its Occipital Bones, Fins, Teeth, and general Appearance.--Contemporaries of the _Holoptychius_.--Sponge-like Bodies.--Plates resembling those of the Sturgeon.--Teeth of various forms, but all evidently the teeth of fishes.--Limestone Band and its probable Origin.--Fossils of the Yellow Sandstone.--the _Pterichthys_ of Dura Den.--Member of a Family peculiarly characteristic of the System.--No intervening Formation between the Old Red Sandstone and the Coal Measures.--The _Holoptychius_ contemporary for a time with the _Megalichthys_,--The Columns of Tubal-Cain, 151-172