GREEN SAND. 



GREEN SAND. 



cent. ; while the lime, when present, seldom 

 exceeds one-half per cent., and the magnesia 

 is rarely more than a mere trace. 



A comparison of the green sand of New 

 Jersey with that of France, shows no essential 

 difference in their chemical nature. 



Green Sand of Havre, in France. 

 Composition. In 100 parts : 



Silica 50 



Alumina ------ 7 



Protoxide of iron - - - - 31 



Poiash ------ 10 



Water 11 



Loss ...... 1 



100 



The late lamented chemist, Dr. Edward Tur- 

 ner, of London, also examined, with great care, 

 the chemical constitution of the green sand of 

 Kent, in England. 



His experiments gave, in the 100 parts ; 



S.licn - - - 



Alumina 



Protoxide of iron - 



Potash --- 



Magnesia 



Water ... 



- 48-5 



- 170 



- 220 



- a trace. 



- 3-8 



- 7-0 



983 



The absence of potash in the green granules 

 of the English green sand, and the large pro- 

 portion of magnesia, are facts not a little re- 

 markable. 



Economical relations of the Green Sand forma- 

 tion. Abundant evidence might be adduced to 

 provt 1 that the true fertilizing principle in marl 

 is not lime, but potash. The analyses which 

 have been made give us, in several cases, no 

 lime at all; and where a small proportion of 

 June is present in the green granular mineral, 

 it is in a combined slate, chemically united 

 with the other ingredients, and not traceable to 

 the organic remains which are in many of 

 these instances not present in the stratum. 

 Besides, the quantity of shelly matter, even 

 where the shells are plentiful, is so dispropor- 

 tionately small, and the matter of the shells 

 often so firm and unsusceptible of that easy 

 disintegration neces>ary to form a calcareous 

 marl adapted to act speedily upon the crop, 

 that the striking effects witnessed from the 

 marl can in nowise be attributed to the trivial 

 amount of lime which the shells may occasion- 

 ally furnish to the land. Nevertheless, as 

 some feebly beneficial effects may possibly 

 arise from this source, it may be of service to 

 the agriculturist in choosing between different 

 fossiliferous marls, to attend to the nature of 

 the particular fossils, and the state of more or 

 less decomposition or change in which they 

 are to be found. 



Selection of Green Sand. For judging of the 

 quality of a marl by observation, says Professor 

 Rogers, "some familiarity with the multiform 

 aspects which it assumes is indispensable. The 

 leading rule, however, is to bear in mind that the 

 fertilizing efficacy of the compound resides in 

 the minute, round, greenish grains which com- 

 pose most, or sometimes all of it; and that it 

 seems, moreover, to be dependent upon the pro- 

 portion in these green grains of those powerful 

 alkaline stimulants to vegetation, potash and 

 , but especially potash. The first thing, then, 



is to approximate to the relative quantity of ths 

 green grains in the whole mass, and this may 

 be effected with a greater or less degree of ac- 

 curacy in several ways. The simplest and 

 readiest method is to employ a small pockel 

 magnifying glass, and to become familiar with 

 the dark green grains, so as to distinguish 

 them at once from other dark varieties of sand 

 which sometimes occur associated with them. 

 A little practice will very soon enable one to 

 use the glass expertly, and to arrive at a pretty 

 true estimate of the probable percentage of the 

 green granules. But as these granules cannot 

 sometimes be distinguished from the grains of 

 ordinary white flinty sand, or from other kinds, 

 in consequence of the particles being all alike 

 coated with a thin film of the dark cementing 

 clay, it will be useful to adopt some method of 

 bringing out, under the magnifier, their differ- 

 ent characteristics of colour and form. Let 

 the mass be washed in a large glass tumbler, 

 and repeatedly agitated with the water, until as 

 much of the clay as possible has been detach- 

 ed from the grains. After pouring off the tur- 

 bid water by repeated rinsings, and permitting 

 it to settle until clear, we may estimate the 

 comparative quantity of clay in different marls 

 by the relative amount of sediment which sub- 

 sides. If we wish to be more accurate, we 

 can weigh out a given quantity of the marl, 

 then pursue the above plan, and decant the 

 clear water from the clay, and after thoroughly 

 drying the clay, weigh it to ascertain its 

 amount. Having got away most of the clay, we 

 should spread out the granular matter upon a 

 sheet of paper and dry it, when there will be 

 no further difficulty in distinguishing, by their 

 colour and lustre, the foreign impurities from 

 the grains of true marl, and also of estimating 

 the relative abundance of each. When the marl 

 to be examined contains much clay, I would re- 

 commend the experiments to be made upon a 

 regularly weighed quantity, weighing both the 

 clayey and the granular portions. A delicate 

 apothecary's balance will commonly be found 

 accurate enough. Another more expeditious, 

 though less accurate method, is merely to dry 

 the marl, spread it extremely thin upon a sheet 

 of white paper, and then hold it near a win- 

 dow, or in the light, to examine it carefully by 

 the magnifier. The flinty sand, though stained 

 with clay, may then be clearly discerned in 

 consequence of its transparency ; whereas, 

 when we inspect a solid lump, all the particles 

 upon the surface are nearly alike dark. 



"A useful suggestion is, to place a portion of 

 the marl upon a hot shovel, or on the top of a 

 stove, when all the granules will change from 

 their ordinary green tint to a light red or brick 

 colour, while the other materials of the mass 

 sustain little alteration. This will often render 

 obvious to the naked eye the proportion of the 

 green grains. 



" When there is a yellowish or whitish in 

 crustation upon the marl after the moist sur- 

 face has remained for some time exposed to 

 the weather, it is indicative of the existence of 

 a portion of either copperas or sulphate of alu 

 mina, the hurtful nature of which has already 

 been explained. 



" An astringent inky taste will very often de 

 3D 589 



