Geological Society of London, 289 



in inducing the bleaching of red beds, the mere reduction of the 

 red peroxide to a lower state of oxide of less colouring power will 

 in none of the cases examined account for the fact of the variegation : 

 an increased proportion of protoxide to peroxide in the bleached 

 portions is rarely found, and a material increase in the amount of 

 protoxide in the bleached portions never occurrs. 



3rd. The bleaching induced by the presence of organic matter, and 

 nearly every form of variegation of red beds, consists in the actual 

 passage of the oxide of iron from the discoloured areas, unaccompanied 

 by any change of combination, excepting the invariable conversion 

 of the anhydrous into the hydrated peroxide. 



4th. The re -arrangement of the iron in variegated beds is not 

 through the agency of dissolution, for it is more frequent in beds 

 coloured with the insoluble peroxide, than where the iron occurs as 

 the more soluble protoxide. 



5th. The dispersion of the peroxide of iron has been in some cases 

 incited under a variety of evident conditions independent of mere 

 chemical reaction, and in other cases precisely similar changes of 

 position of the colouring oxide seem to have taken place arbitrarily, 

 unconnected with any apparent cause or condition ; and again, in 

 some cases the fresh location of the moved peroxide of iron is 

 evident, whilst in others the disposal of the iron removed from the 

 bleached areas is difficult to account for. 



6th. This rearrangement of the colouring peroxide of iron is 

 rarely accompanied by any other change of position or state of 

 combination of the other constituents of the stratum, and appears 

 to be wholly independent of its chemical constitution ; in short, the 

 movement of the iron seems to be inexplicable on any simple 

 chemical theory. 



7th. The motion has sometimes taken place centripetally, the 

 peroxide being aggregated to a nucleus forming the centre of the 

 area of discolouration, and sometimes centrifugally as a ring of re- 

 deposited peroxide around the bleached patch. 



8th. Of the forms of variegation due to simple chemical change, 

 unaccompanied by any movement of the iron, the most frequent is 

 the partial conversion of the Carbonate of protoxide into the 

 hydrated peroxide, and also of the red anhydrous into the yellow 

 hydrated peroxide, and less commonly the secondary formation of the 

 bisulphide ; also the several stages of decomposition of the bisul- 

 phide occurring in mechanical association with the peroxide, in 

 various strata ; and lastly, the infiltration of lime and magnesia into 

 red beds. 



9th. Some of the more complicated forms of variegation of red 

 beds appear to be the joint result of the phenomena of segregation, 

 and changes of combination which may have proceeded simultane- 

 ously or in succession. 



10th. The ferruginous banding of yellow sandstones appears to be 

 the result of the segregation of the hydrous peroxide of iron into lines 

 which are invariably adjacent to a bleached part of the stratum over 

 which they have advanced, gathering up the peroxide of iron in 



