[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 this system at all. There are some of our British geologists, too, who still regard it as a sort of debatable 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 to 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.[C]
[C] 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 lied 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 ten thousand 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.)