GYPSEOUS EARTIL 457 



remain perfect, though neither the shells themselves nor any portion 

 of their calcareous substance remain, as the earth in this part, and 

 where most generally seen, contains not a particle of carbonate of 

 lime. Among the yellow spots there are also other small spots and 

 streaks of reddish brown-coloured clay, very pure, soft and unctuous 

 to the touch. The bright yellow clay is doubtless largely impreg- 

 nated with iron, or is a true ochre. Though soft within the bed, 

 this yellow ochre hardens when exposed to the air on the outside, 

 and even when under water. Many of the yellow spots made by 

 this ochre, as seen on the surface of a smooth section of the bed, 

 have a faint resemblance to the shape of sections of bivalve shells ; 

 and these contrasted with -the general green ground, and with the 

 exception of the colours being different, give to such a section of 

 the bank somewhat the appearance of the beautiful black marble 

 used sometimes for mantel-pieces, in which the white traces of what 

 were formerly shells show throughout. In some places near to and 

 below the beach, the earth is seen much darker coloured, indeed is' 

 almost black when moist in the bank, though more of dark and 

 dull green when dry. This deeper colour is owing to the green 

 granules being present in larger quantity ; and generally, if not 

 always, the lower part of the bed of earth is richer in that ingre- 

 dient than the upper. The empty impressions which were former- 

 ly filled by shells are still found in penetrating below ; but as the 

 depth increases, first are seen some fragments, and then whole shells, 

 though greatly decayed, and the parts having scarcely any coherence. 

 Still, generally, even below, where these shells are most abundant, 

 their quantity would not furnish as much as two per cent., and gene- 

 rally not one per cent., to the whole thickness of the bed; and, 

 therefore, the carbonate of lime, though of course useful in pro- 

 portion to its quantity, can give no appreciable addition of value 

 to the mass as manure. 



Here and there, but rarely, in the upper and dry part of this bed, 

 crystals of gypsum are found, generally so small as to be barely 

 distinguishable by the eye. In the lower and wet part, gypsum is 

 never visible ; but it is nevertheless believed to be always present 

 in some proportion. 



But the important and most characteristic mark of the green 

 earth is present in the black granules called " green-sand," which 

 give colour to the mass. To ascertain tha presence of these gra- 

 nules, let a small sample of the earth or marl supposed to contain 

 them be dried, and then crumbled between the fingers, or, if too 

 hard for that, by being rubbed in a mortar, not too finely and closely. 

 Then take a pinch of the powder between the thumb and finger, and 

 sprinkle it very thinly over a piece of white paper. If any of the 

 separated grains appear black (or green), mash one of them with 

 39 



