72 
It is calculated that the water daily consumed in London 
contains no less than 24 tons of carbonate of lime, or 8,000 
tons per year ; and this must be a mere trifle compared with 
the quantity flowing down the Thames and other large rivers 
in England. If we assume that one-third of the water which 
falls in the form of rain in our own island, after filtering 
through the soil and rocks, again finds its way into the sea, 
which has been found, from observations made with Dalton's 
rain gauge, to be nearly the case, and if we assume that each 
gallon of this water acquires ten grains of carbonate of lime, 
then we should have the enormous quantity of 192,000,000 
of tons, or as much as would cover sixty square miles one 
yard deep, conveyed away annually by this process alone. 
I admit that it is not entirely from these rocks that 
water acquires its lime ; the disintegrated particles of 
other rocks forming cultivated soils is another abundant 
source. It is remarkable that most of our soils become 
exhausted in this valuable material in the lapse of time, 
and agriculturists find the necessity of restoring it as a 
manure. The primitive soil of the Lincolnshire wolds, alike 
with the Derbyshire hills, contains scarcely a trace of car- 
bonate of lime, although they have been formed from rocks 
containing 98 per cent. No other cause can have removed 
this lime than the carbonic acid contained in this rain-water 
constantly filtering through them ; and no other process 
could be more beautiful in nature or more adapted to 
the service of man; for by this very process, operating 
through a series of ages, are the minute portions of silicate 
of potash, iron, alumina, &c, separated from these rocks and 
left as a fertile soil ; and hence the means of support to the 
existing race of animals is obtained, which the simple powder 
of the rocks themselves would never have afforded. How 
long a time this has taken to accomplish, and how much lime 
has been removed, you may conceive, when I state that in 
