GREEN SAND. 



tect the presence of these noxious substances ; 

 at times when no such efflorescence shows it- \ 

 self. If the quantity be too small to betray ! 

 them distinctly to the palate, and we are still 

 in doubt as to their presence, other more 

 rigorous tests are within our reach ; and as 

 these astringent matters are so unquestionably 

 pernicious in their action, it is of importance 

 to have the means of determining in what pro- 

 portion they abound in different marls. This 

 can be effected with precision only by a sys- 

 tematic chemical analysis, but their existence 

 can be made to appear by the following simple 

 tests. Put a small portion of the marl in a 

 flask or other thin glass vessel ; pour upon it 

 some pure water, and heat it moderately ; after 

 causing the water to dissolve in this way as 

 much as possible, remove the heat, and let it 

 settle; then decant the clear fluid into some 

 glass vessel, such as a wine-glass. If there is 

 any copperas present, it will be evident upon 

 adding to the fluid a little lime water, which 

 will produce a milky turbidness that after a 

 little while will become stained of a yellowish- 

 brown colour. The milkiness is owing to the 

 formation of gypsum, and the brown colour to 

 oxide of iron from the copperas. Or, in lieu 

 of this, add a solution of oak bark, and, if cop- 

 peras be present, we shall have a dark inky 

 colour at once produced. 



" A good marl will, upon being squeezed in 

 the hand, fall asunder again, rather than bake 

 into a tough doughy mass ; and upon being 

 left in heaps to dry, will assume a light gray- 

 ish-green colour, and be extremely crumbly. 

 It seems to be a very general characteristic of 

 the better class of marls, that they throw out a 

 white efflorescence or crust upon those grains 

 which are most exposed to the air ; hence the 

 very light colour externally which some 

 heaps of marl possess. This crust I have 

 already shown to consist usually of the sul- 

 phate of lime (gypsum), sulphate of magnesia, 

 and carbonate of lime. A drop or two of 

 strong vinegar, or any strong acid, will pro- 

 duce an effervescence or frothing, if it be the 

 carbonate of lime; and should nothing of this 

 kind take place, we may set it down to be 

 gypsum. Of course, from the minuteness of 

 the quantity of the white coating, much care 

 and accuracy of observation are demanded in 

 doing this, in order to avoid erroneous con- 

 clusions. 



"Marls deemed equally good with the kind 

 showing the efflorescence, very frequently 

 occur, exhibiting none of the white incrus- 

 tation. 



" It does not seem that any general rule can 

 be given for distinguishing the fertilizing pro- 

 perties of a marl by its mere colour, as it must 

 appear from what has been said, that the pe- 

 culiar shade of colour is frequently owing to 

 the colour of the intermingled clay. When 

 the mass, however, is comparatively free from 

 clay or common sand, and consists of little 

 else than the green sand, observations go to 

 show that the rather dark green variety is 

 more potent in its effects than the very light 

 green which sometimes overlies it. 



"The presence or absence of shells I look 

 upon to be a point of but little moment, for I 

 590 



GREEN SAND. 



find that several of the most active marls in 

 the region show no traces of fossils. The 

 whole amount of carbonate of lime in the 

 shape of fossils, and in that of the occasional 

 white incrustation upon the grains, can in very 

 few instances amount to 1 per cent; while, 

 as analysis shows, the lime chemically com- 

 bined with the other ingredients in the green 

 grains, is sometimes 1 per cent,, and the pot- 

 ash nearly 12 per cent." 



Professor Hitchcock, in his Elementary 

 Geology, has given the following tabular view 

 of the analysis of specimens of green sand 

 from different countries : 



Application and effects of Green Sand. The 

 resemblance in composition of green sand to 

 glass, each being composed mainly of silex 

 and potash, is striking. The investigations of 

 Liebig demonstrated the indispensable impor- 

 tance to the groAvth of many plants, and espe- 

 cially to wheat, of silex and potash in that 

 state of commixture called by chemists sili- 

 cate of potash. He even went so far as to de- 

 clare an opinion that one of the best of ma- 

 nures that could be applied to the wheat crop 

 would be a solution of glass. In making this 

 admirable induction, he was, apparently, una- 

 ware of the fact that a natural kind of glass, or 

 silicate of potash, under the form of green 

 sand, had been long spread over the American 

 fields with the most striking advantages to the 

 growth of wheat and other crops. 



The effects of green sand applied as a ma- 

 nure, are strongly set forth in the following 

 extracts from Professor H. D. Rogers's Report 

 of his Geological Survey of New Jersey: 



"Mr. Woolley manured a piece of land in the 

 proportion of 200 loads of good stable manure 

 to the acre, applying upon an adjacent tract of 

 the same soil his marl in the ratio of about 20 

 loads per acre. The crops, which were timo- 

 thy and clover, were much heavier upon the 

 section which had received the marl ; and 

 there was this additional fact greatly in favour 

 of the fossil manure over the putrescent one, 

 that the soil was also entirely free from weeds, 

 while the stable manure had rendered its own 

 crop very foul. 



"This green sand stratum at Poplar Swamp 

 seems to be almost entirely free from any sul- 

 phate of iron or other astringent material, and 

 as a consequence the crops seem not to be 

 scorched by an extra dose, however lavishly 

 applied. 



"There can be no doubt that 20 loads of 

 marl per acre must be regarded as an unne- 

 cessarily bountiful dressing; but computing 

 the relative cost of the two manures, when 

 employed in the ratio above stated, we find a 



