CHAP. XVI.
MUD PRODUCED BY GLACIERS.
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mud, because, as we have seen at p. 239, it has yielded nearMaestricht a human jaw at a depth of 19 feet; and M. Bouefound in it, near Strasburg, the bones of nearly half askeleton, at a depth which he calculated at 80 feet, allowingfor the subsequent denudation of the terraces which havebeen shaped out of it.
In every country, and at all geological periods, rivers havebeen depositing fine loam on their inundated plains in themanner explained above at p. 36, where the Nile mud wasspoken of. This mud of the plains of Egypt , accordingto Professor BischofPs chemical analysis, agrees closelyin composition with the loess of the Rhine. * I havealso shown (p. 237), when speaking of the fossil man ofNatchez, how identical in mineral character, and in thegenera of its terrestrial and amphibious shells, is the ancientfluviatile loam of the Mississippi with the loess of theRhine . Thus we find that loam presenting the same aspecthas originated at different times and in distinct hydro-graphical basins; but there can be no doubt that the loessof the Alps may be traced to the advance and retreat ofthose gigantic glaciers which originated during the glacialperiod, when the Alps were a great centre of dispersion,not only of erratics, as we have seen in the last chapter, andof gravel, which was carried farther than the erratics, butalso of very fine mud, which was transported to still greaterdistances and in greater volume down the principal river-courses between the mountains and the sea.
They who have visited Switzerland are aware that everytorrent which issues from an icy cavern at the extremity of aglacier is densely charged with an impalpable powder, pro-duced by the grinding action to which the subjacent floor of