1868.] MAW VARIEGATED STRATA. 395 



of these beds and the occurrence of mineral veins may perhaps help 

 to throw some light on the agency by which the rearrangement of 

 the iron has been influenced. 



Another peculiar form of variegation occurring in the Keuper Sand- 

 stone, and due to the secondary disposition of copper and iron, is 

 represented in figs. 38 & 39, Plate XV., from the Alderley copper- 

 mine, and consists in the segregation to distinct points, out of a com- 

 mon ground, of carbonate of copper and hydrous sesquioxide of iron. 

 These examples give evidence of a dispersive as well as an aggrega- 

 ting action ; for round each nucleus of copper there is a pale circum- 

 scribing zone from which the iron has been expelled. The iron 

 appears also to have occupied particular centres, from which the 

 copper has in like manner been driven, resulting in a singularly 

 picturesque mottling of brown and blue blotches, with interspersed 

 gradations of green and yellow. 



13. The Variegated Iron-ore Deposits of the Northamptonshire 

 Oolites. — In connexion with the subject of yellow-banded sandstones, 

 reference must be made to the ironstone deposit of Northampton- 

 shire, which illustrates with strongly marked features the same prin- 

 ciple of arrangement. A position has been assigned to it both at 

 the base of the Great Oolite and the top of the Inferior Oolite. The 

 workable bed averages from 12 to 20 feet in thickness. Fig. 37 

 (Plate XY.) represents a portion from the neighbourhood of Ells- 

 worth, compiled from a sketch made on the spot, and some photo- 

 graphs kindly procured for me by my friend Mr. S. Sharp, F.G.S., 

 of Dallington Hall. The whole stratum gives indications of having 

 been completely rearranged since its deposition, even to the almost 

 entire obliteration of its stratified structure. 



Taking the bed en masse, it contains, averaging one part with 

 another, from 25 to 40 per cent, of iron. It consists, for the most 

 part, of a loose earthy friable ground of a bright-yellow colour, ex- 

 hibiting an oolitic structure under the microscope. Its composition 

 is as follows : — 



No. 79. Analysis by Dr. Yoelcker of a friable portion of the North- 

 amptonshire iron ore, near Blis worth : — 



Protoxide of iron 0875 



Sesquioxide of iron 21 '280 



Phosphoric acid 1*030 



Sulphuric acid 0-219 



Silica, lime, alumina, magnesia, &c„ not separately determined 76 596 



Carbonic acid none. 



This was pervaded by hard ferruginous bands having, for the most 

 part, a curious cellular arrangement, with the same disposition as 

 the structure represented in fig. 54; but, instead of occurring at iso- 

 lated intervals on the yellow ground, the entire mass of the stratum 

 is made up of the box-like structures. From mutual pressure in close 

 proximity they have assumed the forms of irregular cubes, sometimes 

 elongated in harmony with the stratification, but occasionally, where a 

 joint appears to have occurred, attenuated in a vertical direction. It is 

 important to notice that the boundary of each cavity is independent 



