>S'. V. Wood— Origin of the Loess. ■ 413 



composed essentially of quartz grains, with a proportion of peroxide 

 of iron enveloping these, and giving colour to the mass, such grains 

 being of dimensions similar to those found to make up the liraon, 

 but associated with, a preponderating number of larger grains. 



From this investigation M. de Mercey comes to the conclusion that 

 the limon, thus originating from the levigation of the flint, had 

 flowed as mud from a sheet of land-ice similar to that of Greenland, 

 which moved over Picardy ; and therefore he designates it " Limon 

 glaciaire ; " but herein in my ojiinion lies his error, for we know by 

 the Chalky clay what the morainic mud was which resulted from 

 land-ice moving over a chalk country. This, where the Jurassic 

 clays as well as the chalk contributed to its constitution, is clay more 

 or less full of rolled chalk, and of flints (besides stones from the old 

 conglomerates,) which are large and subangular, the splinters or 

 angular fragments (eclats) abounding in the Picardy limon, and in 

 the formation which corresponds to it in the South and South-east 

 of England, being altogether absent ; and where, as on the flank of 

 the Lincolnshii'B Wold, the chalk alone has, save to a slight extent, 

 furnished the material, it is so made up of the chalk itself, recon- 

 structed, as to be quite white, and burnt for lime ; whereas this 

 Picardy limon is, according to M. de Mercey, nearly destitute of lime, 

 and formed entirely of flint from the chalk beneath it, disintegrated. 



The true origin of the limon thus described seems to me to 

 receive its explanation in the process referred to in my previous 

 communication, viz. the annual thawing and refreezing of the upper 

 layer of the permanently frozen land surface, which everywhere, 

 save beneath the land-ice, was subjected to the intense cold of an 

 arctic winter. We lack, it is true, what would be important towards 

 a complete demonstration, experimental evidence of the effect on 

 flint of cold like that of a Siberian winter — say from 40° to 70° 

 below zero of Fahr., but it is evident that some cause not now in 

 operation here has ruptured, in the way described, the flint of the 

 Picardy limon, and the flint of which angular fragments are dis- 

 tributed through the corresponding formation of the south and 

 south-east of England, as well as the angular fragments of stone 

 distributed through this in parts, such as Lincolnshire, where it rests 

 on limestone. M. de Mercey assigns the bief a silex as the source of 

 all the siliceous grains and flint eclats of which the limon is made 

 up, but though, from atmospheric agency during the terrestrial 

 interval anterior to the major glaciation, the land surface that 

 remained above the line of the submergence which accompanied this 

 glaciation in Picardy had probably become covered with flints, and 

 from similar agency during the interval between the major and 

 minor glaciations (where, save to the extent that the sea reached up 

 the valleys there, Picardy was all land, and the GyreAia gravel of 

 the Somme overlain by this limon accumulated), the surface of the 

 lower elevations, which had been denuded of the gravel of the great 

 submergence by the waves during the rise from this submergence, 

 and so become bare chalk, may have to some extent become covered 

 with flints, yet I consider the red bief a silex, the brown limon 



