CHAP. xvi. MUD PEODUCED BY GLACIEES. 325 



loess, a step the more necessary, as a French geologist, for 

 whose knowledge and judgment I have great respect, tells 

 me he has come to the conclusion that ' the loess ' is ( a myth,' 

 having no real existence in a geological sense, or as holding 

 a definite place in the chronological series. 



No doubt it is true that in every country, and at all 

 geological periods, rivers have been depositing fine loam on 

 their inundated plains in the manner explained above at 

 p. 34, where the Nile mud was spoken of. This mud of the 

 plains of Egypt, according to Professor BischofT's chemical 

 analysis, agrees closely in composition with the loess of the 

 Bhine.* I have also shown (p. 201), when speaking of the 

 fossil man of Natchez, how identical in mineral character, and 

 in the genera of its terrestrial and amphibious shells, is the 

 ancient fluviatile loam of the Mississippi with the loess of the 

 Ehine. But granting that loam presenting the same aspect has 

 originated at different times and in distinct hydrographical 

 basins, it is nevertheless true that, during the glacial period, 

 the Alps were a great centre of dispersion, not only of erratics, 

 as we have seen in the last chapter, and of gravel, which was 

 carried farther than the erratics, but also of very fine mud, 

 which was transported to still greater distances and in 

 greater volume down the principal river-courses between the 

 mountains and the sea. 



Mud produced by Glaciers. 



They who have visited Switzerland are aware that every 

 torrent which issues from an icy cavern at the extremity of a 

 glacier is densely charged with an impalpable powder, pro 

 duced by the grinding action to which the subjacent floor of 

 rock and the stones and sand frozen into the ice are exposed 

 in the manner before described. We may therefore readily 



* Chemical and Physical Geology, yol. i. p. 132. 



