2 Capt. James on the Variegated Sandstone Systems. 



same distance on either side the great cross lines, a, b (Plate I. 

 fig. 1), whether a fault was produced or not, and this not only 

 in the vertical section, but also along the strata as looking 

 down upon them, at the foot of the cliff, at b, c*. The same 

 appearance, or rather the same fact, may be seen in the Old Red 

 Sandstone in the cliff lower down the Severn near Purton 

 passage ; and it is almost impossible to look at this and not to 

 see that the fissures, whether it be those between the strata, or 

 those which intersect the strata vertically, have acted as chan- 

 nels through which something has been introduced to dis- 

 charge the colour on either side ; but if we arrive at this con- 

 clusion by looking at the matter on a large scale, the exami- 

 nation of the separate slabs brings the fact home to us even 

 more strikingly, for example, in fig. 2. Looking down upon a 

 slab of Old Red Sandstone, which I sketched in company 

 with Professor Phillips, we see cracks extending across it and 

 branching, and this bluish-green colour extending at a nearly 

 equal distance on either side, following every turn and branch, 

 whilst there is no crack or alteration in the structure of the 

 rock at the boundary of the colour. Again, in fig. 3, in marl 

 (and this is a sketch the size of the original), we see the same 

 central crack along the bluish-green colour ; and even this 

 may be sometimes observed in the circular spots (fig. 4), they 

 being the sections of pipes such as one of those in fig. 2. One 

 might multiply such examples to any extent, but enough have 

 been given to establish the fact, that the original red colour has 

 been discharged or altered ; and this has taken place fully to 

 the same extent in the fine sandstones and marl of the Old 

 Red, as it has in those of the new, though perhaps the colours 

 are not so vivid. 



May 15, 1843. Henry James, Capt. R. E. 



Since writing the above, I learn from Mr. Mallet, whose 

 scientific acquirements are so well known, that the colouring 

 matter of these light greenish beds in the New Red Sandstone 

 is the protoxide of iron ; and he says, " If [through] a fissure 

 in a rock containing peroxide of iron a stream of water 

 should pass containing an earthy sulphate and organic matter, 

 the sulphate will be decomposed, and sulphuretted hydrogen 

 evolved, which might reduce the peroxide of iron to a lower 

 oxide." 



This seems to offer the most satisfactory explanation of the 

 chemical action which has taken place, Earthy sulphates 



* In cases where the strata are not equal to twice the distance at which 

 the colour is discharged, the whole stratum will of course appear of the 

 light colour, as at c. 



