I2 BURTON WATERS—DRINKING AND BREWING. 
thus be evident why it is that spring waters are nearly 
always less contaminated than streams, rivers, or open 
reservoirs, and are consequently a safer source of drinking 
water in inhabited districts. Some spring-waters contain so 
little organic matter,—less that one part per 100,000,000 of 
albuminoid and free ammonia together—that it would be 
most difficult to prepare distilled water as pure. 
It may perhaps be as well cto here explain what a spring 
is. Surface water percolating through the soil, and accumu- 
lating in natural underground reservoirs—usually in the form 
of porous strata, interstratified between two impervious 
beds—finds an outlet through a crack or fault in the upper 
bed of impervious material and the overlying strata, or at 
the outcrop of the porous strata, and is pushed to the 
surface by the pressure of the accumulated water in the 
porous strata. Such an escape of water forms a spring, 
and it may be on the surface of the ground or in the bed 
of a river, or below a surface bed of gravel or sand, as is 
the case with many springs below this town. The pressure 
depends upon the volume of water contained in the under- 
ground reservoir, and the slope of the beds forming that 
reservoir. 
Some of our ordinary shallow-well waters are good 
examples of this, consisting of a very hard gypseous water, 
fairly free from organic contamination, which is almost 
entirely spring-water from the underlying marl and sand- 
stone beds; but a very much greater number of our wells 
on the other hand contain a water which is a mixture of 
the ordinary valley drainage with the very hard gypseous 
spring-water above referred to. As the gravel bed acts as 
a filter, and favours the conversion of organic matter into 
salts of ammonia, nitrites and nitrates, our well waters 
nearly all contain these salts in some quantity, and are 
consequently, if not undrinkable, more or less suspicious. 
Well waters as a class must be considered suspicious, and 
