though the ichthyolites of both differed specifically from the ichthyolites of Caithness, which occur chiefly in the middle and upper beds of the formation, and from those also of Lady Cumming of Altyre, which occur, as I have said, at the top. And in examining into the cause, it was found that the two collections, though furnished by localities more than a hundred miles apart, were yet derived, if I may so express myself, from the same low platform, both alike representing the fossiliferous base of the system, and both removed but by a single stage from the great unfossiliferous conglomerate below. Thus there seem to be what may be termed two storeys of being in this lower formation,-storeys in which the groupes, though generically identical, are specifically dissimilar.

CHAPTER VIII.

Upper Formations of the Old Red Sandstone.-Room enough for each and to spare.-Middle or Cornstone Formation.-— The Cephalaspis its most characteristic Organism.-Description. The Den of Balruddery richer in the Fossils of this middle Formation than any other Locality yet discovered.— Various Cotemporaries of the Cephalaspis.-Vegetable Impressions.Gigantic Crustacean.- Seraphim.-Ichthyodorulites. Sketch of the Geology of Forfarshire.-Its older Deposits of the Cornstone Formation.-The Quarries of Carmylie.-Their Vegetable and Animal Remains.-The Upper Formation.-Wide Extent of the Fauna and Flora of the earlier Formations.-Probable Cause.

HITHERTO I have dwelt almost exclusively on the fossils of the Lower Old Red Sandstone, and the history of their discovery: I shall now ascend to the organisms of its higher platforms. The system in Scotland, as in the sister kingdom, has its middle and upper groupes, and these are in no degree less curious than the inferior group already described, nor do they more resemble the existences of the present time. Does the reader remember the illustration of the pyramid employed in an early chapter,-its three parallel bars, and the strange hieroglyphics of the middle bar? Let him now imagine another pyramid, inscribed with the remaining and later history of the system. We read, as before, from the base upwards, but find the broken and half-defaced characters of

the second erection descending into the very soil, as in those obelisks of Egypt round which the sands of the desert have been accumulating for ages. Hence a hiatus in our history, for future excavators to fill; and it contains many such blanks, every unfossiliferous bar in either pyramid representing a gap in the record. Three distinct formations the group undoubtedly contains, perhaps more; nor will the fact appear strange to the reader who remembers how numerous the formations are that lie over and under it, and that its vast depth of ten thousand feet equals that of the whole secondary system from top to bottom. Eight such formations as the Oolite, or ten such formations as the Chalk, could rest, the one over the other, in the space occupied by a group so enormous. To the evidence of its three distinct formations, which is of a very simple character, I shall advert as I go along.

The central or Cornstone division of the system in England is characterized throughout its vast depth by a peculiar family of ichthyolites, which occur in none of the other divisions. I have already had occasion to refer to the Cephalaspis. Four species of this fish have been discovered in the Cornstones of Hereford, Salop, Worcester, Monmouth, and Brecon; "and as they are always found," says Mr Murchison, " in the same division of the Old Red System, they have become valuable auxiliaries in enabling the geologist to identify its subdivisions through England and Wales, and also to institute direct comparisons between the different strata of the Old Red Sandstone of England and Scotland." The Cephalaspis is one of the most

curious ichthyolites of the system.

(See Plate X. fig. 1.) Has the reader ever seen a saddler's cutting knife?—a tool with a crescent-shaped blade, and the handle fixed transversely in the centre of its concave side. In general outline the Cephalaspis resembled this tool, the crescent-shaped blade representing the head, the transverse handle the body. We have but to give the handle an angular instead of a rounded shape, and to press together the pointed horns of the crescent till they incline towards each other, and the convex or sharpened edge is elongated into a semiellipse, cut in the line of its shortest diameter, in order to produce the complete form of the Cephalaspis. The head, compared with the body, was of great size, -comprising fully one-third the creature's entire length. In the centre, and placed closely together, as in many of the flat fish, were the eyes. Some of the specimens show two dorsals, and an anal and caudal fin. The thin and angular body presents a jointed appearance, somewhat like that of a lobster or trilobite. Like the bodies of most of the ichthyolites of the system, it was covered with variously-formed scales of bone; the creature's head was cased in strong plates of the same material, the whole upper side lying under one huge buckler,-and hence the name Cephalaspis, or buckler-head. In proportion to its strength and size, it seems to have been amply furnished with weapons of defence. Such was the strength and massiveness of its covering, that its remains are found comparatively entire in arenaceous rocks impregnated with iron, in which few other fossils could have survived. Its various species, as they

occur in the Welsh and English Cornstones, says Mr Murchison, seem not to have been suddenly killed and entombed, but to have been long exposed to submarine agencies, such as the attacks of animals, currents, concretionary action," &c.; and yet, "though much dismembered, the geologist has little difficulty in recognizing even the smallest portions of them." Nor does it seem to have been quite unfurnished with offensive weapons. The sword-fish, with its strong and pointed spear, has been known to perforate the oaken ribs of the firmest-built vessels; and, poised and directed by its lesser fins, and impelled by its powerful tail, it may be regarded either as an arrow or javelin flung with tremendous force, or as a knight speeding to the encounter with his lance in rest. Now there are missiles employed in eastern warfare, which, instead of being pointed like the arrow or javelin, are edged somewhat like the crooked falchion or saddler's cutting-knife, and which are capable of being cast with such force, that they have been known to sever a horse's leg through the bone; and if the sword-fish may be properly compared to an arrow or javelin, the combative powers of the Cephalaspis may be illustrated, it is probable, by a weapon of this kind,-the head all around its elliptical margin presenting a sharp edge, like that of a cutting-knife or falchion. Its impetus, however, must have been comparatively small, for its organs of motion were so it was a bolt carefully fashioned, but a bolt cast from a feeble bow. But if weak in the assault, it must have been formiIdable when assailed. "The pointed horns of the crescent," said Agassiz to the writer, “seem to have