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example a green-coated flint surrounded by a banded tabular flint, 
showing that the first formed flint must have been in existence as 
a nodule before it received its green coat, and after having become 
coated with glauconite it was surrounded by the after growth of 
tabular flint. This example of the green-coated flint leads to the 
consideration of the mineral that has given, from its colour, the 
distinguishing name to the Greensands, although the particular 
specimen just mentioned is geologically far distant from the forma- 
tion which constitutes the lower cretaceous rocks. 
The mineral Glauconite is chemically a protosilicate of iron 
and potash, and is found coating grains of sand and filling the 
cavities of foraminifera, asin the greensands of the lower Tertiaries ; 
coating flints especially at the base of the Thanet sands, but is absent 
from the black, white-coated flints of the chalk; showing again in 
the Upper Greensand ; oveurring in a very brilliantly green- 
coloured bed with cubical pyrites in the upper Gault clay, present- 
ing a charming mixture of green and gold. And lastly forming a 
conspicuous feature of the Folkestone beds of the Lower Greensand, 
some of the largest particles being found in the bottom bed of the 
Folkestone series with grains of quartz, jasper, Lydian stone, &c. 
As the geological mind is by nature and habit an 
enquiring mind, so the question arises what is glauconite ? 
Chemistry answers, a protosilicate of iron and potash. There is 
plenty of silica and iron in the surrounding beds, but whence the 
potash? Have we not the answer in drift wood, we find 
mineralised in the same beds, and also in the Tertiary beds where 
glauconite gives its colour to the sands ? 
The wood in decomposing reduced the iron to its lower oxide, 
the potash also set free at the same time, would combine with the 
soluble silica, and protoxide of iron, to form the protosilicate of 
iron and potash. This combination having taken place, we find a 
mineral, like green glass, not readily acted upon even by boiling 
concentrated acids, but still decomposed by the mysterious power 
of the vegetable soil, and potash once more appropriated by trees 
and plants. This has been recognised in America, where the 
glauconitic earths have been used as a dressing for land. Thus the 
powers of nature might be typified by the serpent masticating its 
own tail, for the operations of chemical actions taking place 
within the rocks complete their circle of changes in the upper life 
of the vegetable world, and though the colour may be but a mere 
resemblance, it is remarkably the same. 
The beautifully wooded scenery of Saltwood, Sevenoaks, 
Dorking, and the whole range of the Lower Greensand hills, 
bearing a wealth of woodland beauty, testifies to the name not 
having been ill-chosen or misplaced. 
