ECONOMICAL GEOLOGY. 
309 
composition of vegetable, or (especially) animal matter, it is injurious in 
all proportions ; but the brown humous acids, from peat 'and muck beds, 
do not seem to be deleterious even when amounting to saturation. Sea- 
going vessels are 6aid to prefer the brown, wine-colored waters of the 
Dismal Swamp and other such peaty waters of the coast. 
Suspended matters in drinking water are usually unwholesome, and a 
frequent source of disease. 
Nitric acid, ammonia, phosphoric acid and chlorine are commonly in 
dications of pollution, especially the three last named, and waters so con- 
taminated are dangerous to health. The greatest total amount of solid 
matter per gallon in potable waters should not exceed 30, or at most, 40 
grains ; the carbonate of lime should not constitute more than one third 
of that ; the organic matter should not pass one grain, and sulphate of 
lime and magnesia salts should be absent, or if present, only in minute 
quantities. 
Lake and River waters are generally purer than that from spring and 
wells, and for obvious reasons. All waters come from the' ocean by evapo- 
ration, and fall in the form of rain in a state of comparative purity, ab- 
sorbing from the atmosphere, besides the gases of which it is composed, 
the animal, vegetable and mineral dust which floats every where in it, 
and also a minute portion of ammonia, nitric acid, and other matters (sul- 
phurous acid, &c.), thrown into it by the combustion of coal, &c. A part 
of this water, after reaching the surface of the earth, passes directly into the 
rivers and lakes ; another portion penetrates the crevices of the rocks, or 
the porous earth, and makes its way, by a slow underground circulation, 
to the sources of springs, or is tapped by wells, and so comes to the air 
again, charged with whatever soluble mineral matters there may have 
been in the rocks and earths through which it has percolated, so that the 
character of the water so issuing, is determined by that of the rocks. 
Other things being equal, the water is purer in regions characterized by 
the older, crystalline formations, granites, gneisses, &c. 
Mineral waters are simply those which contain either an excess of those 
mineral matters usually found in spring and well water, or (and more 
commonly) such rare substances as are supposed to have valuable medi- 
cinal properties. The following analyses will convey a general notion of 
the composition of such waters. It will be seen that sea water is a most 
conspicuous example of mineral water. 
Ocean Water. 
Dead Sea “ 
gr s. pr. gal. 
. 2,408.00 
. 13,488.10 
