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Show 618 ADDENDA. other facts (p. 381), are quite intelligible to me from the briefness, with which they are alluded to. M. Agassiz says (p. 37 5), "The erratic blocks of the Jura every where repose on polished surfaces, all those at least which have not been carried beyond the ct·est of our mountains, and which have not fallen to the bottom of our longitudinal valleys, as may be seen throughout the valleys of the Creux du Vent. But they do not repose immediately upon these polished surfaces. Wherever the rounded pebbles which accompany the great blocks have not been removed by subsequent influences, it is remarked that small blocks, in other words pebbles of different sizes, form a bed of some inches, and sometimes even of many feet, upon which the great angular blocks repose. These pebbles are also much rounded, even polished, and are heaped up in such a way that the larger are above the smaller, and that the last often pass below into a fine sand, lying immediately over the polished surfaces. This order of superposition, which is constant, is opposed to all idea of a transport by currents ; for in this latter case the order of the superposition of the pebbles would have been precisely reversed." Further on (p. 379) he remarks that the action of the glaciers is immense; " for these masses, continually moving upon each other, and on the surface, bruise and grind down every thing moveable, and polish the solid surfaces on which they repose ; at the same time that they push before them all that they encounter, with a force which is irresistible. It is to these movements (of the great stratum of ice) we must attribute the strange superposition of the rolled pebbles, and of the sand, which immediately reposes upon the polished surfaces ; and it is unquestionably to the grating of this sand upon these surfaces that the fine lines which we find (previously compared to the scratches made by a diamond on glass) arc owing, and which would never have existed, if the sand had been acted upon by a current of water." Now it may be demanded, by what possible means can such violent action arrange the large pebbles above the smaller ones, and these again above the sand? The fact appears to me utterly inexplicable on this view. Again it is said, that the surface of the rock is marked by furrows and gibbosities, as well as by scratches, and that these "never follow the direction of the slope of the mountain, but arc oblique and longitudinal (that is, in the line of the mountain, and therefore nearly horizontal), a direction which excludes every idea of a stream of water being the cause of these erosions." What explanation will it be believed is offered for this fact ?-It is, that the fine lines and furrows "must have resulted from the much greater facility which the ice had in dilating itself in the direction of the great Swiss valley, than transversely, confined as it were between the Jura and the Alps." ! ADDENDA. 619 I will now endeavonr to show how far these very curious facts, which we owe to M. Agassiz's observation, can be explained by the theory of floating ice : and the theory, I may add, if applicable to this case, solves that which presents far greater difficulties, than any other of the kind in Europe. I should first state that I make two assumptions, and if these be rejected, the theory is not applicable to the case of the erratic blocks of the Alps :-first, that an arm of the sea extended between the Jura and the Alps, during that period in which, as I have before shown, it is probable, that the proportional area of water in Europe was greater, and certain, that the productions of the land and water had a more tropical character, at the same time that the snow-line descended lower. The age of the Molasse, which occupies this area, between the Jura anu Alps, has not been accurately determined; but it is supposed to be miocene, and is said to contain leaves of the Chamrerops, a genus of palms, at present found further from the equator than any other kind. It is not, however, evident that the Molasse was deposited by the sea during the latest period, when it occupied a confined limit between the Alps and Jura; but even if this should be found to be the case, it would be rash in auy one positively to conclude that glaciers could not have descended to the shores of a sea, on which the Chamrerops flourished, after that we know they descend in the southern hemisphere so near the limits of several tropical forms. My second assumption is, that the elevation of this much of Switzerland, whenever it took place, was slow and gradual: this is supported by the strongest analogies of South America, Scandinavia, and other parts of the world; whilst on the other hand, the assumption that it had been sudden, would be unsupported by a single ascertained fact in nature. Now, as the numerous masses of ice, which fall from the glaciers at the head of the ~ounds on the South American coast, are slowly drifted outwards (owing to the fresh water flowing in from the foot of the glaciers), and in the more open channels are left to be acted on by the winds and currents; so must it have been with the icebergs from the glaciers of the Alps, situated in the same latitude, and under similar conditions. These icebergs would in most cases be driven on some part of the surrounding shore; but from floating deep they would ground a little way from the beach, and then being packed together, and driven to and fro, as the winds changed, and as the tides rose and fell, would they not, like a glacier on the land, though in a lesser degree, "bruise and grind down every thing and polish the solid surface, on which they reposed?" In the rapids of the North American rivers, over which large bodies of ice are driven, carrying with them pebbles and fragments of rocks, I am informed by Dr. Richardson, that the primitive l'Ocks arc scooped and hollowed, and have their surfaces polished and glossy. Dr. Richardson, however, is not prepared to say, whether this |