mode of arrangement, in place of being scattered, as they generally are, without order through the mass; and vegetable remains would not have been entirely wanting; or so rare, if they do exist. Then there must have been a barrier to contain the waters of the lake, at the head of the delta of the Rhine near Bonn, and that barrier must have been wholly swept away; but a country with forms more unlike those which we might expect, had such a barrier ever existed, can hardly be imagined.

All the appearances of the Rhine valley favour the supposition that, at the time of the deposit of the loess, there was a free river communication between Basle and the sea, and the vertebræ of the Lamna certainly render that supposition more probable. "It may seem very extraordinary that the first remains of fossil fish obtained from this freshwater silt should belong to a marine genus, but M. Agassiz has informed Mr. Lyell that both in the Senegal and the Amazon certain species of the Shark and Skate families (Squalus and Raia, Linn.) have been known to ascend to the distance of several hundred miles from the ocean, and analogous facts are referred to in Margrave and Pisa's Natural History of India *."

In a work descriptive of Bonn and its neighbourhood†, there is the following statement. "The chronicle of Bonn further informs us of a visit to "our river from an animal of the remote north; a sea monster, whose appear"ance may be brought forcibly before our imagination by the steam-boat of "modern days, as it works its way through the waters of the Rhine. In the be

ginning of the year 1680, a Sea Cow, or Walrus, more than fourteen feet in "length, was seen swimming up the Rhine past Bonn. A violent and unheard"of agitation of the water was observed, accompanied by a loud noise, and by "two lofty jets of water spouting from the forehead of the monster. The whole "town rushed to the river to see the great beast, the very name of which was "then unheard of by them. The centinel on the Alten Zoll fired at it several "times but missed it, and the animal proceeded on its way upwards undis"turbed, and is said to have got above Strasburg. Two months afterwards, it "was cast ashore dead, near the village of Niel, about three miles below Co"logne, with four wounds from bullets below the head; but it was not known by whom or where it had been killed."

In the present imperfect state of our knowledge, there seems to be no explanation, upon the whole, so rational as that suggested by Mr. Lyell in the Address above alluded to, who says, "Instead of supposing one continuous

* Geological Society's "Proceedings, " vol. ii. p. 222.

+ Hundeshagen, Die Stadt und Universität Bonn am Rhein, mit ihren Umgebungen. Habicht, Bonn, 1882, p. 15.

"lake of sufficient extent and depth to allow of the simultaneous accumulation "of loess at all heights and throughout the whole area where it now occurs, I "conceive that subsequently to the period when the countries now drained by "the Rhine and its tributaries, acquired nearly their actual form and geographical features, they were again depressed gradually by a movement like that "now in progress on the west coast of Greenland. In proportion as the whole " district was lowered, the general fall of the waters between the Alps and the ocean was lessened, and both the main and lateral valleys, becoming more subject to river inundations, were partially filled up with fluviatile silt containing land and freshwater shells. After this operation, when a thickness of many hundred feet of loess had been thrown down slowly, and in the course of many centuries, the whole region was once more upheaved gradually, but "perhaps not equally, throughout the whole region. During this upward move"ment most of the fine loam was carried off by denudation to such an extent that "the original valleys were nearly re-excavated. The country was thus restored "to its pristine state, with the exception of those patches of loess still remaining, " and which, from their frequency and their remarkable homogeneousness of "composition and fossils, attest the original continuity and common origin of "the whole. By introducing such general fluctuations of relative level, we may dispense with the necessity of erecting and afterwards removing a great "barrier more than 1200 feet high, sufficient to exclude the ocean from the valley of the Rhine during the accumulation of the loess."

Sweden has afforded the most unequivocal proofs that upward and downward movements of the land may take place in countries where no ordinary volcanic action is to be seen; and that so gradually, as to be imperceptible to all who are not watching the phænomenon: and, as there are so many indications of volcanic action in early times, on both sides of the Rhine valley, it does not seem to me to be stretching theory beyond the limits of just philosophical reasoning, to suppose that such oscillations may have taken place in this district, during the gradual accumulation of the loess, and subsequently to its deposition.

END OF VOL. IV.

INDEX.