Mr. Maw on some Chemical Analyses of Variegated Strata. 315 



and in these the sandy agglomeration seems to have given place to a 

 crystalline structure ; but the hardest of those found in situ were 

 resolvable into sand by the action of hydrochloric acid, and ap- 

 peared to be merely held together by a calcareous cement. 



A block resting on the Red Crag near Woodbridge was found 

 on analysis to contain no lime, excepting a small quantity in the 

 form of silicate. 



The springs in the gravel-bed at Crowfield near Coddenham are 

 chalybeate, containing in solution lime and iron, which are pre- 

 cipitated on standing ; and much carbonic acid is evolved from a 

 well sunk through the gravel : the author considered that the 

 carbonic acid may have been the solvent agent in forming the 

 calcareous cement, and that the first stage of the consolidation of 

 the blocks of saccharoid sandstone may have been by the agency of 

 calcareous matter ; and he referred to the possibility of lime in 

 solution, when in contact with silica, giving rise to silicate of lime, 

 a very small proportion of which would form a powerful cement in 

 agglutinating siliceous particles together. 



2. " Notes on some Chemical Analyses of variegated Strata." 

 By George Maw, Esq., F.G.S., F.L.S., &c. 



The author gave thejresults of some analyses for the determination 

 of Iron in the light and dark parts of variegated Slates, Sandstones, 

 and Marls, the colour of which is due to oxide of iron, and of 

 which the variegation appears to be disposed independently of 

 mechanical arrangement. The analysis in each case exhibited the 

 fact that the lighter blotches, spots, and stripes contained a smaller 

 portion of the colouring oxide than the average mass, a proportion 

 which implies an actual difference in the percentage of the metallic 

 iron, and which could not be accounted for by any mere difference in 

 the state of its combination. This shows an actual departure of a part 

 of the colouring oxide out of the colourless patches, and a dispersive 

 process which seemed to be the very reverse of the segregation of 

 nodules of Carbonate of Lime and Carbonate of Iron out of a clayey 

 matrix. Among the forms of variegation referred to were : — (1st) 

 that resulting from the segregation of dark blotches out of a lighter 

 matrix, the evenness of colour of which does not appear to have been 

 materially affected by the withdrawal of a part of its colouring-matter; 

 (2nd) that resulting from the segregation of dark blotches out of a 

 lighter ground, each of which is concentrically surrounded by a distinct 

 and well-defined zone lighter than the general ground ; (3rd) strata 

 variegated with light blotches containing a smaller proportion of 

 colouring-matter than the general ground, but not arranged con- 

 centrically round a darker nucleus ; (4th) the variegation of coloured 

 strata with both light and dark blotches, containing respectively 

 a smaller and larger proportion of the colouring oxide than the 

 general ground, but which are not arranged, a« in the 2nd case, con- 

 centrically with each other. 



