;U2 The American Geoioyits: May, 1896 
the fact finally that whole rivers are seen to disappear in lime- 
stone areas and to issue again at the distance of several kilo- 
meters. 
If we suppose now that the surface waters are replaced by 
mineral waters rising from the depths of the earth we may 
easily understand the existence of layers and levels of mineral 
waters. We see that having followed subterranean or super- 
ficial thalwegs they have produced the deposits that are found 
to-day. Faults have played the role of artesian wells; but 
it is also true that mineral waters under great pressure could 
circulate in all the cavities of the terrestrial crust. There is 
then no difficulty in admitting the circulation of mineral wa- 
ters, either ascending or descending. 
These waters, arising from unknown depths and circulating 
in the joints or fractures, or at the contact of eruptive rocks, 
have next encountered terranes whose strata were either 
highly inclined, approaching a vertical position, or gently in- 
clined and nearly horizontal. In penetrating the joints of 
the former they have formed bed-veins; and following the 
porous beds of the latter they have formed "niveaux" and 
metalliferous thalwegs. 
All forms of deposits may be explained by this circulation 
of mineral waters. The deposits at Laurium owe their origin 
to mineral waters which followed the contacts of schists and 
limestone beds, alternating in nearly horizontal layers. All 
through the Mediterranean basin are found beds of iron ore, 
which have taken the place of limestone, enclosed in an im- 
pervious rock, such as schist or quartzyte; and sometimes 
even yet the course followed by the mineral water may be 
traced. 
Examples of metalliferous "niveaux" are not rare. In 
France may be cited arkose, which surrounds the central plat- 
eau and which contains galena and blende. The beds of ga- 
lena and blende of Figeac (Lot) deposited along the bedding- 
planes of Jurassic limestone which has been but little dis- 
turbed are a striking example of a metalliferous "niveau." 
On the Balearic islands, at Carthaginia in Spain, remarkable 
instances occur. 
In steeply inclined terranes bed-veins or interstratified 
masses are produced. Of this nature are the deposits of Rio 
Tinto, Tharsis, etc., in Spain. 
