1868.] 



MAW VARIEGATED STHATA. 



389 



on a linen cloth), the circuraference of the patch being darker than 

 the general mass, and drying up to a hard line against the unstained 



Fig. 53. — Carboniferous Sandstone, with Ferruginous Bands j 

 Workington, Cumberland. 



portion. I believe the similarity is only resemblance, and that a 

 careful examination of the whole of the phenomena presented by 

 banded yellow rocks will lead to the conclusion that it is independent 

 of any mechanical process. 



One of the most suggestive points is the almost invariable con- 

 tiguity of the lightest to the darkest parts of the strata. In some 

 cases dark ferruginous bands are environed on either side by excep- 

 tionally light portions, which graduate into the general colour of 

 the stone ; but the most frequent arrangement is the bounding of the 

 dark band on one side by white sandstone, and on the other by yellow. 



On any view of mere mechanical arrangement it is impossible to 

 explain this very constant phenomenon, as, if the ferruginous stain 

 was infiltrated into a lighter-coloured rock, the presence of ex- 

 ceptionally light portions, lighter tha7i the average colour of the bed, 

 seems quite unaccountable. 



Pig. 35, PL Xy.*, and figs. 54 and 55, represent two of the simplest 

 forms of this banding and blotching — figs. 35 and 54 consisting of 

 isolated light patches on a uniform yellow ground, separated by a dark 

 ferruginous ring, and fig. 55 of a yellow patch separated by a similar 

 ferruginous band from the lighter ground on which it is placed. In 

 this case the complete isolation of the dark areas of ferruginous co- 

 lour excludes the possibility of their being due to foreign infiltration. 

 Fig. 56 represents a somewhat similar form of variegation, occurring 

 in the Ashdown sands (Wealden), near Hastings ; and determina- 

 tions of the iron in the light and dark portions, made at the Labo- 



* I wish to express my obligations to Mr. Allen for the very successful ex- 

 ecution of PI. XV. by the mezzotint process, which seems peculiarly available 

 for the rendering of subjects with much variety of colour. The whole of the 

 colours on this sheet were worked from two steel plates, with only two separate 

 printings. 



