192 



prevailing colour of the grains is a deep green, though sometimes 

 the tint is as light as that of verdiler. It is often of a dull greenish 

 blue, and not unfrequently of a dark chocolate colour. 



Alonfl- the eastern side of the marl tract in Monmouth, Bur- 

 lington, and Gloucester, the stratum comprises very generally two 

 varieties of the greensand, distinct as to colour, and holding 

 generally the same relative position to each other. The upper- 

 most layer, where it appears (for it is not always present), is of a 

 light and glowing green, having very nearly the hue of the green 

 paint called verdiler; while the lower one is the common dark 

 variety, of a dull bluish-green, or sometimes of a dull blue colour 

 from adhering clay. 



In some instances, particularly where the material constitutes 

 the soil, the granules possess a brownish colour, the consequence 

 evidently of the protoxide of iron which they contain, having 

 undergone upon the surface a change to the condition of the 

 peroxide. The dull colour so usual to the surfaces of these 

 grains, when contrasted with the brighter green within the mass, 

 would appear manifestly to proceed from the same cause. Some 

 shade of green may be pronounced to be the colour essential to 

 this mineral, as all the deviations from this tint are attributable 

 either to oxidation, or to a thin coating of clay, which frequently 

 encrusts each grain, and from which the deposit is rarely al- 

 together free. When a mass of the greensand or " marl" is 

 washed, especially with water (o which a small quantity of an 

 acid has been added, we invariably find the granules assuming a 

 bright green surface. This colour is also produced in all cases 

 when we mash or bruise a grain, no matter what may be its 

 colour externally. By crushing the grains upon a sheet of white 

 paper, we have an easy and unerring test in the colour of the 

 streak, by which to recognise this material from all other varieties 

 of sand. 



Though the green granular mineral here described, constitutes 

 the essential and distinctive ingredient in the greensand stratum, 

 it rarely exists unassociated with several extraneous substances, 

 particularly clay and vhite siliceous sand. These constitute 

 sometimes as large a proportion as fifty per cent, of the bed, 

 causing much variety in its external aspect, and influencing ma- 

 terially its properties as an agricultural agent. The sand which 



