308 Sectional Officers' Reports. 
form, can be found in the catch-pit which first receives the spring 
water, and it is only after having travelled through a length of 
pipe for nearly 1} miles that the crystals appear. 
The usual explanation for lime deposits is that they are due 
to the escape of Carbonic Acid gas just when the water issues 
from the rocks. This at once tends to release some of the lime 
as an insoluble carbonate which had previously been dissolved in 
the water as a soluble bi-carbonate. 
The same explanation answers in the present case, but 
some delicate and unusual conditions are necessary for the growth 
of the crystals. 
The explanation seems to be this:—The water from the 
Marlstone rock contains carbonate of lime in solution; carbonic 
acid gas escapes as soon as the water enters the catch-pit, and 
this at once tends to release some of the lime from solution, This 
release is not completed before the water enters the pipe convey- 
ing it to the tank, and, the lime being in what may be termed its 
nascent condition as it travels gently through the full pipe, takes 
the opportunity to precipitate on to any minute nuclei in the 
water, and builds up its crystalline form of rhombic crystals in 
preference to the amorphous, or sub-crystalline condition which 
would otherwise be the case if the water had remained quiescent 
or open to the atmosphere ; or even if the rate of travel through 
the pipe had been greater. 
The water contains a small quantity of iron in solution 
which begins to oxidise as soon as it reaches the air ; these minute 
and almost imperceptible particles of iron oxide may form the 
nuclei upon which the calcite crystals grow; or it may be that the 
calcite itself is so used, but whatever it is there is no lack of points 
from which the crystals can build. 
It has been my privilege to examine a great number of 
springs and the deposits which they yield under varying conditions, 
but this is the only occasion when perfect rhombs of calcite have 
been noticed. 
