THE METAMORPHISM OF ROCKS. 
233 
mathematics, by the integration of the infinitesimally small, real 
and absolute quantities are obtained ? Tyndall, in his examina- 
tion of the origin and probable destiny of the Niagara falls, 
when speaking of the wear and tear due to running water, states 
that time and intensity are the principal factors of geological 
change, and, to a certain extent, convertible into each other. A 
weak force acting during a long period, and a more intense one 
acting during a shorter period, may approximately produce the 
same effect. The sand-blast, invented by Quincey, is an example 
of the concentration of force in space ; and the reciprocal action 
of steel and flint, an illustration of the same principle. Although 
the total amount of heat produced by striking softer substances 
with each other, such as calc-spar and lead, may be even greater, 
the generation of a spark requires a local concentration of heat. 
This local concentration of heat is also obtained in electro-calo- 
rific actions. By the use of a Voltaic pile of 2000 pairs, Sir H. 
Davy succeeded in melting platinum ; and though it can be 
demonstrated that, in a given time, the chemical action taking 
place in this pile is far from being equivalent to the fuel con- 
sumed in the same time in a blast-furnace, the heat generated 
in the latter is insufficient to melt the platinum- wire, which 
melts after being exposed for some seconds between the elec- 
trodes of the Voltaic pile. The Voltaic arc acts similarly to a 
powerful blowpipe, which heats and melts in rapid succession 
the particles of platinum ; whereas, in a blast-furnace, the heat 
generated cannot accumulate in a given point, and therefore is 
incapable of melting the platinum, i.e., of producing, in each of 
its molecules, the number of vibrations which are necessary for 
its melting. 
If the possibility of calorific effects of the electric currents 
is admitted in the same manner as the electrochemical effects 
are already universally accepted for the purpose of explaining 
the slow reactions which operate in the earth’s interior, all the 
principal difficulties presented by local and contact metamor- 
phism disappear, and it then becomes possible to explain, with- 
out having need of any violent theory, such notable cases as, 
for example, that of the Blaue Kuppe, near Eschwege, to which 
Delesse repeatedly draws attention in his Etudes sur la Meta- 
morphisme. In that locality, well known to geologists, is found 
a basaltic conglomerate which encloses a great number of small 
fragments of a variegated sandstone, which are all vitrified on 
their outside. This effect cannot be attributed to the basalt, 
because the heat retained by such a comparatively small mass 
would not have been sufficient to melt the exterior of the 
sandstone fragments. Delesse, therefore, arrives at the conclu- 
sion that an agent more subtle than the basalt has penetrated 
the sandstone, and produced the same liquidity by fusion. 
