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fifty, the quantity of carbon contained in most woods, this having 
been replaced by forty per cent. of phosphate of lime. The source 
of the phosphates is probably the highly fossiliferous over-lying 
Gault clay. 
We have here an instance of action and results similar to the 
circulation of blood in the animal, building up bone and muscle ; 
and also to the circulation of sap in the vegetable, producing woody 
fibre; for circulating water passing through these beds has caused 
animal matter to be replaced by pyrites, and the carbon of the 
wood by phosphate of lime. 
In the laboratory of nature the chemical changes take place 
so slowly and in such dilute solutions that the chemist may well 
say that he has not the time, however much he may have the 
inclination, to study them. We are too apt to forget that 
substances which we regard as insoluble, such as sulphate of 
barytes and tricalcic phosphate, as well as silica, are soluble in the 
water that is slowly but constantly passing through the rocks. It is 
in this manner that pebbles have been formed in the vesicles of old 
lavas, thus composing amygdaloid traps; and zeolites have been pro- 
duced inside cavities in bricks forming part of the structure of ancient 
baths. In the same manner we find crystals in the drusic cavities 
of flints, showing how water carrying mineral matter in solution 
has passed through the very surface and substance of the flint. I 
believe in this sense it is no figure of speech to say that stones 
grow, and in a double sense it may be taken that they grow both 
larger and smaller. 
Underneath some of our railway arches we may see stalactites 
that have grown by the percolation of water, five or six inches 
in five and twenty years, but the very water that has caused them 
to grow by bringing lime in solution may dissolve them away 
again when it has no more lime to bring. Indeed it may be said 
that in nature there is nothing so constant as change. The very 
mountains may be increasing or diminishing in height through 
chemical changes going on in their interiors as well as from other 
causes. 
In this manner, from the interchange of mineral particles 
carried on in a continuous circle of changes between organic and 
inorganic atoms, those cherty bands of limestone in the Lower 
Greensand may have been formed, not necessarily under the sea, 
but after the beds became land, though not the conventional dryland 
that we so often hear about and which so seldom exists. 
Mr. G. Dowker, F.G.S., in an able paper read before the East 
Kent Natural History Society, some years ago, ascribes the forma- 
tion of flint in veins and bands to similar causes, and gives as an 
