8. V. Wood — Origin of the Loess. 411 



Y.— Further Eejiarks on the Origin of the Loess. 

 By Sbakles V. Wood, F.G.S. 



IN a previous communication to this Magazine I suggested that 

 the Loess originated from the thawing and refrigeration, during 

 the major and minor glaciations, of the upper layer of the soil, 

 which, where it was unprotected by land ice, was permanently 

 frozen to a great depth ; such layer having a sliding motion which 

 caused the material to accumulate in the hollows, and so expose 

 continually to this action over the rest of the surface, fresh subsoil 

 which had been previously permanently frozen. I now supplement 

 this by a particular examination of the way in which such process 

 appears to me to have acted in originating that part of the Loess 

 which is represented by the "Limon," or brickearth, of Picardy. 



With this "limon" I have no personal acquaintance, but it has 

 been made the subject of a very careful and minute description by 

 M. de Mercey, in the '•' Bulletin Mensuel " of the Linnean Society 

 of the North of France, for the years 1874-5 ; and from such 

 description the facts detailed below are exclusively derived. 



M. de Mercey first glances at the different views taken by geolo- 

 gists as to this formation, viz., that of M. Elie de Beaumont, who 

 referred the part of it which occupies the plateaus, to the " Ancient 

 alluvia of Bresse, of the Pliocene formation," and the part which 

 occupies the valley slopes to the " modern superficial deposits ; " 

 that of M. D'Archiac, who regarded the limon on the plateaux and 

 on the valley slopes as " one and the same deposit, termed by him 

 ancient alluvium posterior to the rolled flints with Klephas primi- 

 genius, and forming the last term of the Quaternary series ; " and 

 that of Mr. Prestwich, who regarded " the limon of the slopes as 

 due to successive inundations at the different levels of the gravels, 

 and its age, like that of the gravels, proportionately more recent as 

 its level was lower, and, with the gravel it covered, as being con- 

 nected with the excavation of the valleys, but distinct from the 

 limon on the plateaux, the reconstruction of which had furnished 

 part of the material for that on the slopes, and the formation of 

 which dated back to the Pliocene epoch." 



He then describes minutely the character and description of this 

 limon, insisting himself that it is all of one mode of formation, and 

 of one period, viz., " the last term of the Quaternary series," (what- 

 ever that may mean,) "covering the ancient alluvia" (i.e. the gravels 

 of the Somme valley,) "and all other deposits except the modern," 

 He adds that though of small thickness on the valley slopes, and low 

 elevations, it is sometimes upwards of ten metres thick on the higher 

 parts of the plateaux, that it is yellowish in colour, and " hiefenx " 

 with flint fragments towards its base. Everywhere it is unstratified. 



The chief fact which strikes us, he says, is the particular breaking 

 up of materials derived from the formation on which the limon rests, 

 and their dissemination in its base. This subjacent formation in the 

 neighbourhood of Amiens is the chalk with flints, and angular frag- 

 ments (" eclats ") of these flints are scattered through the limon which 



