CHAPTER II.

The Old Red Sandstone.-Till very lately its Existence as a distinct Formation disputed. Still little known.—Its great Importance in the Geological Scale.-Illustration.-The North of Scotland girdled by an immense Belt of Old Red Sandstone.-Line of the Girdle along the Coast.—Marks of vast Denudation.-Its Extent partially indicated by Hills on the Western Coast of Ross-shire.-The System of great Depth in the North of Scotland.-Difficulties in the way of estimating the Thickness of Deposits.-Peculiar Formation of Hill.-Illustrated by Ben Nevis.-Caution to the Geological Critic.-Lower Old Red Sandstone immensely developed in Caithness.-Sketch of the Geology of that County. Its strange Group of Fossils.-Their present place of Sepulture. Their ancient Habitat.-Agassiz.-Amazing Progress of Fossil Ichthyology during the last few Years.Its Nomenclature.-Learned Names repel unlearned Readers. Not a great deal in them.

"THE Old Red Sandstone," says a Scottish geologist, in a digest of some recent geological discoveries, which appeared a short time ago in an Edinburgh newspaper, "has been hitherto considered as remarkably barren of fossils." The remark is expressive of a pretty general opinion among geologists of even the present time, and I quote it on this account. Only a few years have gone by since men of no low standing in the science disputed the very existence of this

formation-system rather, for it contains at least three distinct formations; and, but for the influence of one accomplished geologist, the celebrated author of the Silurian System, it would have been probably degraded from its place in the scale altogether. "You must inevitably give up the Old Red Sandstone," said an ingenious foreigner to Mr Murchison, when on a visit to England about four years ago, and whose celebrity among his own countrymen rested chiefly on his researches in the more ancient formations,-" you must inevitably give up the Old Red Sandstone: it is a mere local deposit, a doubtful accumulation huddled

up in a corner, and has no type or representative abroad." "I would willingly give it up if nature would," was the reply; "but it assuredly exists, and I cannot." In a recently published tabular exhibition of the geological scale by a continental geologist, I could not distinguish the system at all. There are some of our British geologists, too, who still regard it as a sort of debateable tract, entitled to no independent status. They find, in what they deem its upper beds, the fossils of the Coal Measures, and the lower graduating apparently into the Silurian System; and regard the whole as a sort of common, which should be divided as proprietors used to divide commons in Scotland half a century ago, by giving a portion to each of the bordering territories. Even the better-informed geologists, who assign it its proper place as an independent formation, furnished with its own organisms, contrive to say all they know regarding it in a very few paragraphs. Lyell, in the first edition of his admirable elementary work, published only two

years ago, devotes more than thirty pages to his description of the Coal Measures, and but two and a half to his notice of the Old Red Sandstone.*

* As the succinct notice of this distinguished geologist may serve as a sort of pocket-map to the reader in indicating the position of the system, its three great deposits, and its extent, I take the liberty of transferring it entire.

OLD RED SANDSTONE.

"It was stated that the Carboniferous formation was surmounted by one called the New Red Sandstone,' and underlaid by another called the Old Red, which last was formerly merged in the Carboniferous System, but is now found to be distinguishable by its fossils. The Old Red Sandstone is of enormous thickness in Herefordshire, Worcestershire, Shropshire, and South Wales, where it is seen to crop out beneath the Coal-Measures, and to repose on the Silurian Rocks. In that region its thickness has been estimated by Mr Murchison at no less than 10,000 feet. It consists there of

"1st, A quartzose conglomerate, passing downwards into chocolate-red and green sandstone and marl.

"2d, Cornstone and marl (red and green argillaceous spotted marls, with irregular courses of impure concretionary limestone, provincially called Cornstone, mottled red and green; remains of fishes).

"3d, Tilestone (finely laminated hard reddish or green micaceous or quartzose sandstones, which split into tiles; remains of mollusca and fishes).

"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, Arca, 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

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 zoological 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 Etna over the level of the sea, and in which it contains three distinct groupes 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

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 bucklerheaded, 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, 3, 4.)

of Edward III. down to the present day, but bearing no record of the Williams, the Henries, 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.

At

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. 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 beOn the east there are considerable gaps, as along the shores of Aberdeenshire. The sandstone,

tween.