Geological Society. 157 



goes to prove that the circumstance of the surfaces of contact of con- 

 tiguous elements of the fluid having the same velocity constitutes 

 no objection to the reality of such resistance. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 74.] 



April 15th, 1868. -Sir R. I. Murchison, Bart, K.C.B.,F.R.S.,&c, 

 Vice-President, in the Chair. 



The following communications were read : — 



1. " On the Disposition of Iron in variegated Strata." By 

 George Maw, Esq., F.G.S. 



In this paper the author gave detailed descriptions of the pheno- 

 mena of variegation in rocks of various ages and composition, with 

 numerous analyses of the differently coloured portions. The con- 

 clusions at which he had arrived were the following: — (1) That 

 the assumed production of the colouring-matter of red beds from the 

 decomposition of Iron Pyrites appears untenable. (2) That the 

 bleaching of red beds by the reducing action of fossil carbonaceous 

 matter will not account for the facts of variegation. (3) That this 

 bleaching and nearly every form of variegation of red beds are caused 

 by the passage of iron from the discoloured areas, unaccompanied 

 by any change of combination, excepting the invariable conversion 

 of the anhydrous into the hydrated peroxide. (4) That the arrange- 

 ment of the iron has not been produced by solution. (5) That it 

 has in some cases been produced by a variety of evident conditions 

 independent of mere chemical reaction, while in other cases it seems 

 to have occurred arbitrarily. (6) That it is unaccompanied by any 

 other change in the combination or position of the constituents of 

 the stratum, and appears to be wholly independent of its chemical 

 constitution, any simple chemical theory being, in short, insufficient 

 to account for the movement of the iron. (7) That the motion has 

 sometimes taken place centripetally and sometimes centrifugally. 

 (8) That the partial conversion of the carbonate of protoxide of 

 iron into hydrated peroxide is one of the most frequent purely 

 chemical causes of variegation. Other causes are the conversion of 

 the red anhydrous into the yellow hydrated peroxide, the secondary 

 formation of the bisulphide and the several stages of its decomposi- 

 tion in mechanical association with the peroxide, and, lastly, the 

 infiltration of lime and magnesia into red beds. (9) That some of 

 the more complicated forms are due partly to segregation, and partly 

 to changes of combination. (10) That the ferruginous banding of 

 yellow sandstones is 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 appear to have ad- 

 vanced, gathering up the peroxide of iron in their course, and leaving 

 behind them a depleted area. 



