122 ' Chronicles of Science. [Jan., 



as hydrous sesqnioxide, carbonate of protoxide, and as silicates. 

 Mr. Maw inclines to the opinion that the red sesquioxide was the 

 primary condition of iron in red beds, rejectinj:^ Dr. Dawson's 

 hypothesis that the sesquioxide was derived from the oxidation of 

 bisulphide of iron under the influence of heat and moisture. 



The bleaching of red beds and the pale blotches which so 

 frequently occur in the midst of the j^rimordial colom* are invari- 

 ably due to the abstraction of the colouring oxide, and in most 

 cases ajtpear to be entirely independent of any predisposing cause. 

 The majority of examples of variegation in which there are neither 

 mechanical nor segregated nuclei present, exhibit no difierences in 

 the light and dark parts, merely as regards the p'oioortion of u'on 

 present, neither is there any change in the composition of the 

 matrix, nor any alteration in the state of combination, except the 

 invariable conversion of the red anhydrous into the hydrous sesqui- 

 oxide. Of variegation m connection with joints or cracks, there are 

 two distinct forms : one connected with surface infiltration, in 

 which, along the line of joint, beds containing carbonate of pro- 

 toxide of iron have become charged with the apparently insoluble 

 sesquioxide; and the other, in which rocks coloured by the red 

 sesquioxide have become bleached by its conversion into the pro- 

 toxide. 



The generally accepted theory, suggested by De la Beche, of 

 the bleaching power of fossil carbonaceous matter by its reducing 

 action upon the colouring oxide is not considered sufficient by ]\[r. 

 Maw. Analyses lead to the conclusion that in these cases variega- 

 tion results from a rearrangement of the iron, and not from its loss 

 in a soluble condition, and that this rearrangement sometimes takes 

 place centripetally and at others centrifugal ly. 



The cause which has produced the banding of yellow sand- 

 stone seems to have been that instead of the hydrous peroxide of 

 iron accumulating in spherical nuclei, the segregation has taken 

 place in hues which have gradually advanced, gathering up the 

 peroxide in their jjrogress, and leaving behind them the bleached 

 sandstone deprived of its iron. 



The conclusions at which the author has arrived are that a very 

 small proportion of the forms of variegation can be accounted for 

 by the mere altered state of combination of iron, in situ, the altera- 

 tions of the red anhydrous sesquioxide into hydrous sesquioxide, 

 the reduction of sesquioxide to protoxide of iron, and occasionally the 

 change of colour due to the decomposition of bisulphide of iron, 

 completing the list of colour alterations due to a merely chemical 

 change. Neither will the presence of organic matter account for 

 the changes; and the author concludes that the transference of the 

 colouring matter has taken place by the simple mechanical agency 

 of segregation, principally, and also by infiltration and dissolution. 



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