Represents the Old Red System of Scotland from its upper beds of Yellow Quartzose Sandstone to its Great Conglomerate base. _a._ Quartzose Yellow Sandstone, _b._ Impure concretionary limestone enclosing masses of chert, _c._ Red and variegated sandstones and conglomerate. These three deposits constitute an upper formation of the system, characterized by its peculiar group of fossils. (See Chapter IX.) _d._ Deposit of gray fissile sandstone which constitutes the middle formation of the system, characterized also by its peculiar organic group. (See Chapter VIII.) _e._ Red and variegated sandstones, undistinguishable often in their mineral character from the upper sandstones, c, but in general less gritty, and containing fewer pebbles, _f._ Bituminous schists, _g._ Coarse gritty sandstone. _h._ Great Conglomerate. These four beds compose a lower formation of the system, more strikingly marked by its peculiar organisms than even the other two. (See Chapters II. III. IV. and V.) In the section this lower formation is represented as we find it developed in Caithness and Orkney. In fig. 5 it is represented as developed in Cromarty, where, though the fossils are identical with those of the more northern localities, at least one of the deposits, _f_, is mineralogically different--alternating beds of sandstone and clay, these last enclosing limestone nodules, taking the place of the bituminous schists. SECTION II. The Old Red System of England and Wales, as given in the general Section of Mr. Murchison, with the Silurian Rocks beneath and the carboniferous limestone above. _i._ The point in the geological scale at which vertebrated existences first appear. The three Old Red Sandstone formations of this section correspond in their characteristic fossils with those of Scotland, but the proportions in which they are developed are widely different. The tilestones seem a comparatively narrow stripe in the system in England; the answering formation in Scotland, _e, f, g, h_, is of such enormous thickness, that it has been held by very superior geologists to contain three distinct formations--_e_, the New Red Sandstone, _f_, a representative of the Coal Measures, and _g, h_, the Old Red Sandstone. SECTION III. Interesting case of extensive denudation from existing causes on the northern shore of the Moray Frith. (See pages 197 and 198.) The figures and letters which mark the various beds correspond with those of fig. 5, and of the following section. The "fish-bed," No. 1, represents what the reader will find described in pp. 221-225 as the "platform of sudden death." SECTION IV. Illustration of a fault in the Burn of Eathie, Cromartyshire. (See pages 204 and 205.) EXPLANATIONS OF THE PLATES.