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POPULAR SCIENCE REVIEW. 
According to his idea, this agent was water ; but De 
Castro considers it not more venturous to attribute the pheno- 
mena of the Blaue Kuppe to the calorific action of the electro- 
chemical and electrodynamical currents, produced by that same 
water infiltrating into the sandstone, or by the different tempe- 
rature of the contact rocks, or by any other of the many causes 
which incessantly originate analogous currents. For the expla- 
nation of local metamorphism, extending over large districts 
situated at a great distance from the fluid interior of the earth 
or the eruptive rocks, and sometimes containing interstratified, 
not altered rocks, the hydrothermal theory cannot be admitted 
without exaggerating the physical properties of the substances, 
and attributing to them properties which we are not aware of. 
But in the case of local metamorphism, all effects due to mole- 
cular action are observed — effects, which are all capable of pro- 
ducing electro-telluric currents. An electrical current, by 
whatever cause produced, be it by the contact of two rocks of a 
different temperature, or the slow circulation of water more or 
less charged with other substances, or the very act itself of 
rending or Assuring the earth’s crust by the contraction or 
sliding of the rocks, or the presence of some organic substance 
in the layers of the formation, or many other causes, can circu- 
late with more or less resistance through the whole of the ter- 
restrial mass and will only cease when, according to the law of 
the indestructibility of forces, it is changed into another force 
which manifests itself by thermal, chemical, or mechanical 
effects. Becquerel explains by electricity many phenomena of 
cementation which are observed in nature ; and if one compares 
his simple and reasonable theory with that proposed by Plattner 
as an explanation of the formation of ‘ kernels/ when calcining 
certain cupriferous minerals, it is not possible to doubt about 
the real cause which produces ‘kernels’ containing 40 per cent 
of copper in the calcination of the Rio Tinto ore, of which 
even the richest portion seldom reaches 8 per cent. The electro- 
telluric actions may have played an important part in a num- 
ber of geological phenomena, in the formation of the nodules 
and bands of flint in the Chalk, differently explained by Gaudry, 
Hebert, and d’Orbigny ; the grains of oxide of iron in the Ter- 
tiary ; the oolitic iron-ore in the Jurassic deposits ; the sphero- 
siderite of the Carboniferous formation and the geodic iron ore of 
the modern formation ; the kidneys of phosphorite, which ap- 
pear in distinct geological epochs ; further, in the concentrical 
structure of certain limestone rocks and calcareous minerals ; 
the tendency of rocks to assume a spherical form ; the curious 
formation of embossed pebbles ; the eaglestones, septaria, and 
other phenomena, during a considerable time considered merely 
as lusm naturae ; the formation of agates, the delicate layers 
