GREEN SAND. 



GREEN SAND. 



"In some instances, particularly where the | 

 material constitutes the soil, the granules pos- j 

 sess a brownish colour, the consequence evi- j 

 dently of the protoxide of iron which they con- } 

 tain 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 es- 

 sential to this mineral, as all the deviations 

 from this tint are attributable either to oxida- 

 tion or to a thin coating of clay, which fre- 

 quently encrusts each grain, and from which 

 the deposit is rarely altogether free. When a 

 mass of the green sand or ' marl' is washed, 

 especially with water to 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 distinc- 

 tive ingredient in the green sand stratum, it 

 rarely exists unassociated with several extra- 

 neous substances, particularly clay and white 

 giliriims sand. These constitute sometimes as 

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

 causing much variety in its external aspect, 

 and influencing materially its properties as an 

 agricultural agent; the sand, which is generally 

 white or semi-transparent quartz, existing usu- 

 ally in relatively small amount, the clayey 

 matter being ordinarily the most abundant. 

 This latter is of several tints, but is commonly 

 of a light gray or lead colour. It is also occa- 

 sionally chocolate coloured, brown, and even 

 nearly white. Coating frequently the surfaces 

 of the green grains, it conceals their true colour, 

 imparting its own hue to the entire mass. As 

 it is somewhat adherent when moist, it gives to 

 the stratum where it is abundant the character 

 of a partially plastic clay. Besides the white 

 sand and this clayey material, we often find a 

 minute quantity of finely divided mica mingled 

 with the green sand." (Report of Geological 

 Survey of New Jersey.) 



Professor Rogers gives several analyses of 

 specimens of green sand obtained from pits in 

 various parts of the region where this mineral 

 abounds near the surface of the ground. In 

 some of the beds the green sand is mixed with 

 proportions of clay and common quartzose 

 sand, while in others, although ten per cent, of 

 clay may be present, no common sand is per- 

 ceptible. Besides the clay and common sand 

 usually present with the green sand in the ge- 

 neral mass, there occur occasionally several 

 other substances, "which, though comparative- 

 ly minute in quantity, are," observes Professor 

 Rogers, " possessed of active properties. Some 

 of these materials are probably deleterious, 

 while others are undoubtedly beneficial in their 

 action upon vegetation. The substances re- 

 ferred 'to are carbonate of lime, sulphate of iron 



(copperas), sulphate of alumina, sulphate of 

 lime, arid sulphate of magnesia; also phosphate 

 of iron. 



" They appear to be derived, mainly, at least, 

 from constituents in the clay, and only very 

 partially, if at all, from elements in the green 

 sand itself. 



'The carbonate of lime, in most instances, 

 we can trace to fossil shells and other organic 

 remains, imbedded in the stratum. The sul- 

 phate of iron obviously proceeds from the 

 action of the atmosphere and moisture on the 

 sulphuretof iron, so abundant in the clay; and 

 the sulphate of alumina from the union of a 

 portion of the sulphuric acid thus developed 

 with the argillaceous earth of the clay; while 

 the sulphates of lime and magnesia may result, 

 either from the combination of the same acid 

 with some of the lime and magnesia, sometimes 

 present in a minute share in the green mineral, 

 or, more probably, from its reaction on the car- 

 bonates of lime and magnesia, existing, like 

 the sulphuret of iron, in an insulated state 

 The phosphate of iron is no doubt derived from 

 phosphoric acid, traceable to the animal re- 

 mains, acting on oxide of iron. 



"Several of these substances develope them- 

 selves upon the mass of the marl after il has 

 been dug and exposed to the atmosphere, in the 

 form of a white efflorescence, encrusting alike 

 the clayey matter and the granules of green 

 sand with a delicate crystallization, resembling 

 a light frost. Collected and carefully examined 

 and analyzed, this efflorescence will be found 

 almost invariably to consist, when it is of a 

 pure white, of either the sulphate of magnesia 

 or sulphate of lime (gypsum), the latter predo- 

 minating; and sometimes these two occur 

 united. In some instances, we recognise it to 

 contain the sulphate of magnesia (Epsom salts) 

 in sufficient quantity to be distinguishable by 

 its taste. A yellowish tint and an astringent 

 flavour are apparent when it consists chiefly 

 of the sulphates of alumina and iron. The 

 carbonate of lime more generally shows itself, 

 not in the shape of an efflorescence on the sur- 

 face, like the others, but dispersed in minute 

 granules throughout the body of the marl. 

 Many of these calcareous granules are grains 

 of dolomite, analogous in composition to the 

 magnesian variety of the limestone, which 

 overlies the green sand; whence, probably, the 

 true source of the sulphate of magnesia above 

 referred to. When the traces of shells are 

 very numerous in the bed, and their conversion 

 into the sulphate of lime has happened on the 

 large scale, the gypsum forms a conspicuous 

 part of a soft, white, clayey matter, derived 

 from the shells and interspersed among the 

 green grains. The mixed mass of carbonate 

 and sulphate of lime is then usually in a yel- 

 lowish-white, chalky condition. Sometimes we 

 may detect the gypsum in the marl in the 

 shape of small regular crystals of transparent 

 selenite, at times so minute as only to be de- 

 ; tected by the magnifier. 



"Various fossil shells, and other marine or- 

 ganic remains, amounting to considerably more 

 than one hundred species, are scattered through 

 the green sand. These collections of fossils 

 ' would seem to be most abundant in those parts 



587 



