180 T. S& Hunt on the Chemistry of Natural Waters. 
limonite point to such a reaction. That it is not more abundant 
in solution, is due to the fact that, unlike most other metallic — 
om 
bination with silica. The formation of bauxite, a mixture df — 
hydrate of alumina with variable proportions of hydrous per | 
oxyd of iron, which forms extensive beds in the Tertiary sedi | 
ments of the great Mediterranean basin, indicates a solution of 
alumina on a grand scale, and perhaps owes its origin to thede 
composition of solutions of native alum by alkaline or earthy | 
carbonates. Emery, a crystalline anhydrous form of alumina, — 
has doubtless been formed in a similar manner. See this Journal, — 
, [2] xxxii, 287. The existence in many localities of an insoluble | 
sub-sulphate of alumina, websterite, in layers and concretionary — 
masses in Tertiary clays, evidently points to such a proces 
Compounds consisting chiefly of hydrated alumina are frequently 
found in fissures of the chalk in England. On the absenee of 4 
free hydrated alumina from soils, see Muller, cited in this Jour — 
nal, [2] xxxv, 292. 4 
ous waters, whether of subterranean springs, or of tropical sé 
marshes and lagoons. ‘he reaction between the'sulphurets thus 
formed and the salts or oxyds of iron, copper and similar me 
a may be ; 
from se 
lumi ulphuret of iron, and the alkali as 4 double 
uminous silicate. eo 
f surface 
a 
4 
] 
. We have thus far considered the composition 0 och 
waters as modified by the decay of vegetation, or by the pee 
tween the matters derived from this source and the per™ thus 
sediments. Not less important, however, than the elements 
3 
