It is held by a class of naturalists, some of them of the highest standing, that the skulls of the vertebrata consist, like the columns to which they are attached, of vertebral joints, composed each, in the more typical forms of head, as they are in the trunk, of five parts or elements,—the centrum or body, the two spinous processes which enclose the spinal cord, and the two ribs. These cranial vertebræ, four in number, correspond, it is said, to the four senses that have their seat in the head: there is the nasal vertebra, the centrum of which is the vomer, its spinal processes the nasal and ethmoid bones, and its ribs the upper jaws; there is the ocular vertebra, the centrum of which is the anterior portion of the sphenoid bone, its spinal processes the frontals, and its ribs the under jaws; there is the lingual vertebra, the centrum of which is the posterior sphenoid bone, its spinal processes the parietals, and its ribs the hyoid and branchial bones,—portions of the skeleton largely developed in fishes; and, lastly, there is the auditory vertebra, the centrum of which is the base of the occipital bone, and its spinal processes the occipital crest, and which in the osseous fishes bears attached to it, as its ribs, the bones of the scapular ring.

It had been long known to the continental naturalists, that in certain Russian deposits, very extensively developed, there occur in considerable abundance certain animal organisms; but for many years neither their position nor character could be satisfactorily determined. By some they were placed too high in the scale of organized being; by others too low. Kutorga,—a writer not very familiarly known in this country,—described the remains as those of mammals;—the Russian rocks contained, he said, bones of quadrupeds, and, in especial, the teeth of swine: whereas Lamarck, a better known authority, though not invariably a safe one,—for he had a trick of dreaming when wide awake, and of calling his dreams philosophy,—assigned to them a place among the corals. They belonged, he asserted, as shown by certain star-like markings with which they are fretted, to the Polyparia. He even erected for their reception a new genus of Astræ, which he designated, from the little rounded hillock which rises in the middle of each star, the genus Monticularia. It was left to a living naturalist, M. Eichwald, to fix their true position zoologically among the class of fishes, and to Sir Roderick Murchison to determine their position geologically as ichthyolites of the Old Red Sandstone.

When engaged in prosecuting the self-imposed task of examining in detail the various fossiliferous deposits of Scotland, in the hope of ultimately acquainting myself with them all, I extended my exploratory ramble, about two years ago, into the Mainland of Orkney, and resided for some time in the vicinity of Stromness.

This busy seaport town forms that special centre, in this northern archipelago, from which the structure of the entire group can be most advantageously studied. The geology of the Orkneys, like that of Caithness, owes its chief interest to the immense development which it exhibits of one formation,—the Lower Old Red Sandstone,—and to the extraordinary abundance of its vertebrate remains. It is not too much to affirm, that in the comparatively small portion which this cluster of islands contains of the third part of a system regarded only a few years ago as the least fossiliferous in the geologic scale, there are more fossil fish enclosed than in every other geologic system in England, Scotland, and Wales, from the Coal Measures to the Chalk inclusive. Orkney is emphatically to the geologist what a juvenile Shetland poetess designates her country, in challenging for it a standing independent of the “Land of Cakes,”—a “Land of Fish;” and, were the trade once fairly opened up, could supply with ichthyolites, by the ton and the shipload, the museums of the world.

Several thousand years ago, ere the upheaval of the last of our raised beaches, there existed somewhere on the British coast a submarine bed, rich in sea-weed and the less destructible zoophytes, and inhabited by the commoner crustaceæ and molluscs. Shoals of herrings frequented it every autumn, haunted by their usual enemies the dog-fish, the cod, and the porpoise; and, during the other seasons of the year, it was swum over by the ling, the hake, and the turbot. A considerable stream, that traversed a wide extent of marshy country, waving with flags and reeds, and in which the frog and the newt bred by millions, entered the sea a few hundred yards away, and bore down, when in flood, its modicum of reptilian remains, some of which, sinking over the submarine bed, found a lodgment at the bottom. Portions of reeds and flags were also occasionally entombed, with now and then boughs of the pine and juniper, swept from the higher grounds. Through frequent depositions of earthy matter brought down by the streamlet, and of sand thrown up by the sea, a gradual elevation of the bottom went on, till at length the deep-sea bed came to exist as a shallow bank, over which birds of the wader family stalked mid-leg deep when plying for food; and on one occasion a small porpoise, losing his way, and getting entangled amid its shoals, perished on it, and left his carcase to be covered up by its mud and silt.

The hollows formed on the surface of the earth by the ground sinking or rising, earthquakes, streams of lava, the intersection of strata, and those that occur along the edges of the different formations, are generally filled with water, and constitute systems of lakes, some salt and some fresh. Many of the former may be remnants of an ancient ocean left in the depression of its bed during its retreat as the continents arose.

Almost all lakes are fed by springs in their beds, and they are occasionally the sources of the largest rivers. Some neither receive tributaries nor have outlets: the greater number do both. The quantity of water in lakes varies with the seasons everywhere, especially from the melting snow on mountain chains and high latitudes, and between the tropics from periodical rains. Small lakes occur in mountain passes, formed by water which runs into them from the commanding peaks: they are frequently, as in the Alps, very transparent, of a bright green or azure hue. Large lakes are common on tablelands and in the valleys of mountainous countries, but the largest are on extensive plains. The basin of a lake comprehends all the land drained by it; consequently it is bounded by an imaginary line passing through the sources of all the waters that fall into it.

There are more lakes in high than in low latitudes, and in this respect there is a great analogy between the northern plains of the two principal continents.