1868.] MAW VARIEGATED STRATA. 361 



In some examples of this class of variegation the dark nuclei 

 occur in such close contiguity that the whole of the original red 

 ground seems to have been exhausted, leaving a uniformly light field 

 containing the dark spots of segregation irregularly disposed. In 

 some portions of the Millstone -grit the individual nuclei of the re- 

 arranged sesquioxide of iron are so small that they give portions of 

 the sandstone a freckled appearance, lighter than the general red 

 ground, ^ath which they alternate in irregular blotches. This is 

 seen in the Carboniferous sandstone (Millstone-grit ?) that overlies 

 the Mountain-limestone at Lamanby and Blencow, near Penrith, 

 of which the Penrith station is built. Some of the larger dark 

 blotches are also nuclei of segregation; but most of them are 

 mechanically rounded lumps of soft ha)matite, occurring both in 

 the red and the discoloured portions. Such a combination of me- 

 chanical and secondary causes occasionally produced some singularly 

 complex arrangements of colour, which at a first glance are difficult 

 to understand. 



The points to be particularly noticed with reference to the Coal- 

 port example are, 1st, that the bleached zone appears due to the 

 withdrawal of the colouiing sesquioxide from the red ground into 

 the central nucleus, the one containing less and the other more than 

 the normal colour, and, 2ndly, that there is no evidence of change in 

 the state of combination of the iron, except that the segregated ses- 

 quioxide becomes hydrous. In all three shades of colour the iron 

 principally occurs as sesquioxide ; and the slight differences of the 

 proportions of protoxide and sesquioxide are so irregular that they 

 appear unconnected with the variegation. 



Some remarkable forms of this tricoloured variegation occur in the 

 Gres des Yosges, or Upper Permian, of the East of Prance. Pig. 6 

 (Plate XI.) represents an example of fissile flagstones from the south 

 of Eaon I'Etape, Yosges, in which bleached layers occur ranging 

 with the stratification, accompanied by the rearrangement of the 

 sesquioxide of iron as dark nuclei in the bleached bands ; and in 

 some stones of the Gres bigarre or Lower Trias in the basement of 

 the Palace of Industry, Paris (fig. 12, Plate XII.), the red sesqui- 

 oxide has become converted into the yeUow hydrous sesquioxide, 

 accompanied by its segregation into nuclei which are ranged in lines 

 near the boundary of the area of discoloration. 



The Lower Bagshot beds near Wareham (fig. 23, Plate XIII.) pre- 

 sent some complicated arrangements of colour due to secondary 

 causes, of a somewhat similar character. The primordial bright red 

 colour of these variegated beds was evidently due to anhydrous ses- 

 quioxide of iron ; this has assumed the hydrous condition in irregular 

 yeUow blotches, and in places it has become segregated into a mul- 

 titude of small nodular concretions, surrounded by light-grey bleached 

 zones from which the iron has been abstracted ; by this process a 

 singularly beautiful mottling of four distinct colours has been pro- 

 duced out of an original uniformly red bed. 



A precisely similar form of variegation exists in the Neocomian 

 beds in the neighbourhood of Beauvais, France, where fields of bright 



