"I have already observed that fossils are rare in marls and sandstones in which the red oxide of iron prevails. In the Cornstone, however, of the counties above mentioned, fishes of the genera Cephalaspis and Onchus have been discovered. In the Tilestone, also, Ichthyodorulites of the genus Onchus have been obtained, and a species of Dipterus, with mollusca of the genera Avicula, Area, Cucullæa, Terebratula, Lingula, Turbo, Trochus, Turritella, Bellerophon, Orthoceras, and others.

"By consulting geological maps, the reader will perceive that, from Wales to the north of Scotland, the Old Red Sandstone appears in patches, and often in large tracts. Many fishes have been found in it at Caithness, and various organic remains in the northern part of Fifeshire, where it crops out from beneath the Coal formation, and spreads into the adjoining northern half of Forfarshire; forming, together with trap, the Sidlaw Hills and valley of Strathmore. A large belt of this formation skirts the northern borders of the Grampians, from the sea-coast at Stonehaven and the Frith of Tay to the opposite western coast of the Frith of Clyde. In Forfarshire, where, as in Herefordshire, it is many thousand feet thick, it may be divided into three principal masses—1st. Red and mottled marls, cornstone, and sandstone; 2d. Conglomerate, often of vast thickness; 3d. Tilestones, and paving-stone, highly micaceous, and containing a slight admixture of carbonate of lime. In the uppermost of these divisions, but chiefly in the lowest, the remains of fish have been found, of the genus named by M. Agassiz Cephalaspis, or buckler-headed, from the extraordinary shield which covers the head, and which, has often been mistaken for that of a trilobite of the division Asaphus. A gigantic species of fish, of the genus Holoptychius, has also been found by Dr. Fleming in the Old Red Sandstone of Fifeshire."—Lyell's Elements, pp. 452-4.

It will be found, however, that this hitherto neglected system yields in importance to none of the others, whether we take into account its amazing depth, the great extent to which it is developed both at home and abroad, the interesting links which it furnishes in the zoölogical scale, or the vast period of time which it represents. There are localities in which the depth of the Old Red Sandstone fully equals the elevation of Mount Ætna over the level of the sea, and in which it contains three distinct groups of organic remains, the one rising in beautiful progression over the other. Let the reader imagine a digest of English history, complete from the times of the invasion of Julius Cæsar to the reign of that Harold who was slain at Hastings, and from the times of Edward III. down to the present day, but bearing no record of the Williams, the Henrys, the Edwards, the John, Stephen, and Richard, that reigned during the omitted period, or of the striking and important events by which their several reigns were distinguished. A chronicle thus mutilated and incomplete would be no unapt representation of a geological history of the earth in which the period of the Upper Silurian would be connected with that of the Mountain Limestone, or of the limestone of Burdie House, and the period of the Old Red Sandstone omitted.

The eastern and western coasts of Scotland, which lie to the north of the Friths of Forth and Clyde, together with the southern flank of the Grampians and the northern coast of Sutherland and Caithness, appear to have been girdled at some early period by immense continuous beds of Old Red Sandstone. At a still earlier time, the girdle seems to have formed an entire mantle, which covered the enclosed tract from side to side. The interior is composed of what, after the elder geologists, I shall term primary rocks—porphyries, granites, gneisses, and micaceous schists; and this central nucleus, as it now exists, seems set in a sandstone frame. The southern bar of the frame is still entire: it stretches along the Grampians from Stonehaven to the Frith of Clyde. The northern bar is also well nigh entire: it runs unbroken along the whole northern coast of Caithness, and studs, in three several localities, the northern coast of Sutherland, leaving breaches of no very considerable extent between. On the east, there are considerable gaps, as along the shores of Aberdeenshire.[D] The sandstone, however, appears at Gamrie, in the county of Banff, in a line parallel to the coast, and, after another interruption, follows the coast of the Moray Frith far into the interior of the great Caledonian valley, and then running northward along the shores of Cromarty, Ross, and Sutherland, joins, after another brief interruption, the northern bar at Caithness.

[D] The progress of discovery has shown, since this passage was written, that these gaps are not quite so considerable as I had supposed. The following paragraph, which appeared in July, 1843, in an Aberdeen paper, bears directly on the point, and is worthy of being preserved:—

"ARTESIAN WELL.

"The greatest of these interesting works yet existing in Aberdeen has just been successfully completed at the tape-works of Messrs. Milne, Low, and Co., Woolmanhill. The bore is 8 inches in diameter, and 250 feet 9 inches deep. It required nearly eleven months' working to complete the excavation.

"In its progress, the following strata were cut through in succession:—

6feetvegetable mould.
18"gray or bluish clay.
20"sand and shingle, enclosing rolled stones of various sizes.
6"light blue clay.
3"rough sand and shingle.
115"Old Red Sandstone conglomerate, composed of red clay, quartz, mica, and rolled stones.
74"alternating strata of compact, fine-grained Red Sandstone, varying in thickness from 1 to 7 feet, and clay, varying from 6 inches to 12 feet thick.
8"9 inches, mica-slate formation, the first two feet of which were chiefly a hard, brown quartzose substance, containing iron, manganese, and carbonate of lime.
250feet,9 inches.