18G8.] MAW VARIEGATED STRATA. 373 



The ferruginous nuclei contain : — 



(Analysis No. 55) Protoxide of iron 0474 per cent. 



(Hydrous) sesquioxide of iron SO-.'jSS „ 



Organic matter doubtful traces. 



Water of combination 7 72 percent. 



The neutral grey zones immediately adjacent to the nuclei of 

 segregation contain only about yV^h of the proi)ortion of iron in 

 these centres, viz. : — 



(Analysis No. 54) Protoxide of iron 0254 per cent. 



Sesquioxide of iron 3'779 ,, 



Organic matter slight traces. 



The grey portions mottled -with ochreous yellow contain : — 



(Analysis No. 57) Protoxide of iron 0*294 per cent. 



Hydrous sesquioxide 3*502 „ 



Organic matter slight traces. 



There is also the light-pink-coloured clay, through which the 

 normal red graduates to the grey in the middle of the bed, and 

 which occurs outside the grey zones surrounding the nuclei ; and 

 here we find the iron occurring in a proportion intermediate between 

 that in the grey and that in the full red-coloured clay, viz. : — 



(Analysis No. 56) Protoxide of iron 0-254 per cent. 



Sesquioxide of iron 5*686 ,, 



Organic matter 0*790 „ 



Looking at these analyses, and the relative arrangement of the 

 several colours, it is impossible to resist the conclusion that the 

 excess of coloiu* in the dark parts above the average composition, 

 and its diminution in the adjacent light parts below the avemge, 

 must be due to the actual passage of the iron to the centres of 

 segregation. Here also, as in most other cases of segregation, the 

 motion of the sesquioxide of iron is accompanied by its becoming 

 hydrous, the blood-red of the ground being exchanged for a rich 

 ochreous brown in the nuclei, and bright-yellow rust partially stains 

 the exhausted portions. There is one point in connexion with the 

 variegation of these mottled clays which seems difficult to explain 

 satisfactorily, viz. the existence, about the ferruginous nuclei in 

 the grey ground, of small patches of the blood-red clay quite unal- 

 tered, neither depleted nor enriched. 



Among other cases of variegation apparently connected with the 

 presence of organic matter, the follo^ving may be referred to. Fig. 

 25 (Plate XIII.) represents a yellow surface-clay containing frag- 

 ments of black carbonaceous matter, adjacent to which the clay has 

 been bleached of a pale-grey tint. 



Analyses of the grey and yellow portions gave the following 

 results : — 



