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Show 152 NEWER PLIOCENE PERIOD, [Ch. XI. often containing calcareous sandy concretions o~ nod~les, rare~y excee dm. g t h e s1· ze of a man's head · Its entire thickness., In certa1· n 1o ca} 1' t1' es, a mounts to several hundred feet; yet no signs of strat I' fi ca t1' 0 n appear in the mass, except here and there at the bottom, where there is a slight inte.rmixture. of materials derived from subjacent rocks. No marme r:m.ams are. anywhere imbedded in it, but land-shells of extstzng speczes are extremely common, and the remains of the mammoth, horse, and some other quadrupeds, are said to have been found in it. 'l'he general absence of fresh-water shells is very remarkable. 1 collected a few specimens in the section near the Manheim gate of Heidelberg, and they are mentioned as having been found at a few other spots, by several of the writers above cited. The loess sometimes rises to the height of 300 feet above the alluvial plain of the Rhine, and to the height of 600 feet above the sea; but it is confined to the valley of the Rhine and its tributary valleys, preserving everywhere the same mineral characters, except where the lowest portion is mixed up, as beforementioned, with matter derived from the underlying rocks. The loess reposes on every rock, from the granite to the gravel of the plains of the Rhine, and ll_l~·st have been thrown down from some vast body of water, densely charged with sediment, after the country had assumed its present.· configuration. I am informed by M. Studer, that it does not extend into Switzerland, so that we may suppose the flood to have descended from near the borders of that co~n!ry, perhaps from the neighbourhood of Basle, into the valley of the Rhine, where one of the first great obstacles to its passage would be the Kaiserstuhl, a small group of volcanic hills which stand almost in the middle of the plains of . the Rhine, south of Strasburg, between the chains of the Black Forest and the Vosges. These hills are covered nearly to their . summits with loess. But the narrow gorge of Bingen and Andernach would cause the greatest obstruction, even if we suppose that defile to have been open when the flood descended, which was probably the case, Ch. XI.] LOESS OF TilE VALLEY OF TilE RHINE. 153 since we find the loess lower down the valley, on the flanks of the Siebengebirge. "\.V e have stated that stratification is almost entirely wantiug, but the movement of the muddy waters appears in some places to have torn up the subjacent soil, and then to have thrown down again the foreign matter, thus mingled with the loess, in layers and strata. An alternation of gravel and loess has resulted from this cause in the lower part of the section before alluded to at Heidelberg. I observed a similar blending of the loess, and the variegated sandstone and red marl underlying it at Zeuten and Odenau, in a valley on the right bank of the Rhine, at a short distance fwm the Bergstrasse, between Wiesloch and Bruchsal, a locality pointed out to me by Professor Bronn. Near Andernach there is a similar intermixture and alternation of the lower beds of loess, with volcanic ejections such as are strewed over that country, a phenomenon from which some observers have too hastily inferred that the volcanic eruptions and the deposition of the loess were contemporaneous. The Rhine throughout a great part of its course between the lake of Constance to the falls of Schaffhausen traverses a tertiary deposit, called in Switzerland molasse, which consists in some places of stratified yellow loam. At Stein, near CEningcn, this loam is 150 feet thick, and resembles exceedingly the loss before described, except in being regularly stratified. If we could suppose the waters of a great lake like that of Constance to have been suddenly let free by an earthquake, and in their descent into the valley of the Uhine to have intersected such strata, we might imagine the waters to have become densely charged with loam, with which they may have parted as soon as their velocity was diminished by spreadinO' over a WI'd er space. 0 rrhe catastrophe which brought down the loess must for a time, have desolated the country, but, in the end, it has . enriched the soil, constituting the most fertile parts of Alsace |