striæ are now below the waters. These results, although opposed, are not, as they may at first appear, contradictory; and it is here that the observation of shells completes the study of erratic phenomena, properly so called, by shewing us the chronological order of these events. In fact, the barnacles of Uddevalla, and the serpulas of Christiania, which are found, the former at the height of 200, and the latter of 170 feet above the sea, prove irresistibly that the coast has sunk in those places; the fact that these animals are adhering to striated rocks, shews not less certainly that the rocks were dry before these animals were living there; whence I read this double conclusion, 1st, that the graving of the rocks was anterior to the epoch of the barnacles and serpulas; and, 2d, that, to receive these animals, the coasts of Uddevalla and Christiania must have sunk as far, at least, as would be equivalent to the actual height of these fossils.

But the barnacles and serpulas are not the only proofs of this subsidence. At a much greater height we find shells, over these polished and striated rocks, imbedded in the diluvium; and as the species are in general indigenous, and probably contemporaneous with the serpulas and barnacles, it follows, of course, that the submergence must have been considerable, and equal, at least, to the site of the highest shells of the diluvium (800 feet). This submergence must, consequently, have taken place between the epoch of the furrowing and the stratification of the diluvium. At that time, the glaciers having quitted the plain to retire to the interior mountains, the waters of the sea invaded the low country of Scandinavia, surrounding the solid masonry of the Scandinavian mountains with an ocean to which we shall be able to fix some approximate limit when we are acquainted with the boundaries of the region of diluvial shells. In passing, I would remark, that the analogy of the erratic blocks of Finland with those of Scandinavia, allows us to believe that at that time the Gulf of Bothnia was not separated from the Arctic Sea.

We have no means of determining the length of time which elapsed between the retiring of the glaciers, and that subsiding of the land which led to the invasion of the sea. However the perfect preservation of the polishing beneath the

diluvium, would seem to prove that the period could not have been long. Nowhere are the grooves and scratches more distinct, than where they have been uncovered by removing the diluvium; they usually form a striking contrast with those rounded rocks, whose surface has been for a long time exposed to the wearing effects of the atmosphere.* But as we have no reason to suppose that the action of the atmospheric agents was formerly less energetic than now, I am compelled to believe that the preservation of the polished surfaces under the diluvium, is owing to their having been exposed only a comparatively short time to wear from these agents. It is even probable that the invasion of the sea was one of the causes which have been active, if not decisive, in the destruction of the great glaciers. It explains, at the same time, the colder character of the diluvial fauna; for a mass of ice so considerable could not be melted without materially chilling the waters which bathed it. The cold having slowly disappeared, the temperature would have been gradually elevated, and the fauna of the waters would take by degrees the more temperate character which distinguishes it at the present day.

To this epoch of the invasion of Scandinavia by the waters of the sea, we should refer the arrangement in beds of the mud, sand, and gravel, which the great glacier has left in place, in testimony of its ancient extent. The action of waves coming in upon this moveable soil, has here overturned and heaped up the debris of marine life upon the shore, where the remains are found mingled with scratched rocks and pebbles. If such is really the origin of these deposits, there is no reason for surprise that the scratched pebbles should be so numerous. The waves, in striking them against each other, would wear them more or less; and if blocks of a considerable size have generally better preserved their markings

* We may believe, that if, after a new deluge, the boulders which are at present exposed, should be covered again with gravel, the geologists of future ages would have much more trouble in ascertaining the causes which have produced the effects, than we have at the present day, aided as we are by the preservations, frequently admirable, of the polishing, furrows, and fine striæ.

than the pebbles, it is because, from their weight, they were less exposed to being moved and rolled. It is very natural in Switzerland, where the action of the waters has been less manifest and less prolonged, that the striated pebbles should be more numerous. Thus you do not find there, or only occasionally, distinct beds in the properly glacial deposits. Those which are met with, ordinarily occur in the neighbourhood of torrents.*

After this epoch of immersion, even the proximate duration of which it is impossible at present to ascertain, the country of Scandinavia was again elevated. The shores bordering the high central regions, the plains of Sweden, and those of Finland, were successively raised from the bosom of the waters, bringing back with them to the surface the same mud, the same diluvial gravel, which had been deposited by the glaciers, and which had undergone no other change in the interval than that of being irregularly stratified and mingled with shells. The depressions of the land alone remained covered with water, and formed the lakes of Sweden and Finland, as well as the Gulf of Bothnia. The last, isolated from the ocean by the uprising of the intermediate land, has lost, by degrees, its saltness; and this explains the character of its fauna, which is rather the fauna of brackish water than that of the sea. The interior lakes, also, were transformed completely into fresh water, and here and there may perhaps be found some indications of their ancient condition. It appears that certain fishes, in particular, have resisted these changes in the water; and, according to researches of Scandinavian zoologists, especially of Mr Esmark, the trout of Swedish lakes (Salmo trutta, L.) is only a species of salmon, like the Salmo salar, L. But as the salmon of the coast does not ascend into the lakes, we are naturally led to the conclusion, that this fish has resisted the modifications that have occurred where it dwells. The emersion of land does not take place alike in all parts; the beautiful observations of Messrs Keilhau and Bravais upon the ancient marks of the level of the Scandinavian sea, teach us that there it was

* Voy. Rod. Blanchet, Terrain erratique alluvien du Cassin du Leman. VOL. XLIII. NO. LXXXV.-JULY 1847.

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not uniform throughout. Finally, if it is true that the osars, which may be traced a long distance into the interior, and whose mode of formation we have explained above, indicate successive sea-shores, it follows that the Gulf of Bothnia was once much larger than at present. A large belt of coast now under cultivation, was then under water, and only gradually became elevated.

This successive retreat of the waters has taken place mostly during the present epoch, as undeniable traces of man* are found in the interior of osars. It is probable that during this period of slow emersion, there lived in Scandinavia a prinitive people, an entirely different race, as their osteology indicates, from that of recent Scandinavia, and whose skeletons are found in the peat beds mingled indiscriminately with those of animals, some of which have completely disappeared from the surface of the earth, such as the Bos urus, and others, which are no longer known in the same countries, as the rein-deer.†

Conclusion. It follows, from the preceding considerations, that, whilst the upheavals of Scandinavia are of great importance in the study of erratic blocks, the latter furnish us, in their turn, with valuable hints as to the time and the geological bearing of these elevations. I have shewn that the elevations are not confined to the historical epoch, but extend far back into the period of the diluvium. On the other hand, we learn, from the same examinations, that these elevations have not been continuous; that, on the contrary, they were intermitting and in sweeps, since the land is successively raised and depressed. We have distinguished, in this connection, three principal points; 1st, an epoch when the land was higher than now, the epoch of the glaciers; 2d, a general sinking of the plains of Scandinavia, bringing with it an irruption of the sea; 3d, the rising of the same plains, which is even now in operation.

* See Lyell upon the proofs of a gradual elevation of the soil in certain parts of Sweden.

I am indebted to the beautiful work of Messrs Wilson and Eschricht for these details.

Each of these periods must have had a considerable duration. We can readily believe that, while an agent is acting so slowly that a glacier might transport, for hundreds of leagues, the stones and gravel taken from the Norwegian mountains, a long time must have been required, whose minimum of years would be thousands, if the movement of glaciers, in our day, be regarded as a criterion.

The second period must have been at least as long, if we consider the time required for the existence, propagation, and death of an entire fauna, whose numerous remains are found upon a land once submerged.

Finally, the third period comprehends the historical epoch, when the country was inhabited by the foreign race whose remains are discovered in the peat beds.

It follows, therefore, that the glacier epoch is not merely an accident in the history of our globe, but it embraces a long period, the more important to the geologist, that it is the connecting link between the antediluvial times and the historical era.

On the Meaning originally attached to the term "CAMBRIAN SYSTEM," and on the evidence since obtained of its being geologically synonymous with the previously established term "LOWER SILURIAN." By Sir RODERICK I. MURCHISON, G.C.ST.S., V.P.G.S., F.R.S., &c.

["By such proofs (organic remains) we are enabled to distinguish the Silurian deposits from all others previously described, and through every lithological change we can thereby separate the System into Upper and Lower divisions."—Silurian Syst., p. 9.]

In a communication upon the Silurian rocks of Sweden, published in the preceding number of the Quarterly Journal of the Geological Society, I stated my objections to some opinions of Professor Sedgwick, contained in the previous volume, which suggested a re-arrangement of the recognised divisions of the Upper and Lower rocks of the Silurian system. I was then chiefly called upon to point out the inapplicability of the proposal to remove the Wenlock formation (or a great part of it) from the Upper to the Lower Silurian; for even down to last year Professor Sedgwick had invariably spoken of all the lower paleozoic fossils of North Wales and Cumberland as