Notes on chemical geology
Authors: Taylor Andrew 
Published: December 2013

No true geological theory can be established which ignores the action of those physical and chemical forces which act on our earth in common with the other heavenly bodies. The essential unity of the cosmos has received fresh confirmation from the recent labours of astronomic spectroscopists. It becomes, then, the knight of the hammer not to ignore the bearings of such inquiries on his own science, the more especially as the great terrane revolutions manifested by the volcanic and earthquake activities of the last two years have given such investigations an universal interest.

Recent researches have shown that most of our deductions on the internal condition of the earth have been founded on incomplete data. Arago’s formula of the rate of increase of internal temperature, derived from observations made in the artesian well at Grenelle, does not hold universally. The increment of temperature appears to depend on a variety of conditions, such as the nature of the strata, their saturation or otherwise, the proximity of great bodies of water, and such like.

Many observations go to show remarkable coincidences betwixt the presence of magnetic currents, and such phenomena as volcanoes and earthquakes. M. Perrey has observed that seismic shocks occur with more or less violence according to the moon’s distance from our planet. If these earth disturbances are the outcome of certain aberrations of those electric currents which we know daily pervade the whole surface of our globe, then accurate observations become necessary, that the character of these periodic perturbations of regular currents may be duly appreciated. Mr Mallet’s observations go to prove that earthquake phenomena follow in pretty regular cycles of periodicity—periods of intense disturbance generally occurring at intervals of forty years, being most violent towards the close of the century; and when thus violent, the intensity appears to vary, in different hemispheres, with the month that the earth is nearest or furthest from the sun.

That magnetism varies in intensity throughout the earth, as well as that it has done so in historic time, are two well-known facts. Over two well-defined regions the needle deflects from the true magnetic meridian in two distinctly opposite directions; and Arago has shown that within the last 200 years the direction of deflection has been proved to have altered both in London and Paris. If the sun is the source of the daily earth currents, as Dr Lloyd of Dublin has shown,

*

such facts will not surprise us, knowing as we now do the very variable character of the sun’s body. The lines and periods of magnetic intensity follow the course of the sun until it reaches the full meridian. The epoch of maximum intensity of the current is earliest in islands or places nearly surrounded by the sea, and latest in the interior of great continents. The electricity of the earth is negative, and that of the atmosphere is positive. The cause of the separation of these two kinds of electricity is evaporation; and the intensity is usually greatest on the coasts of great continents, especially when the coast lines are in or near the meridian. The evaporation from the surface of the sea being much greater than from the land, the electricity will be most deficient at the former; hence, besides the electricity due from solar influences alone, there will be a flow of electricity from land to sea. Might not the drought of last summer, prevailing as it did nearly over the surface of our globe, have so deranged the equilibrium of the earth currents as to have caused internal action?

That even well-known physical agencies can aid such currents in producing powerful effects on the crust of the globe is manifest from the fact that condensed steam, where 967 degrees of free heat becomes latent, is a source of electricity. The hydroelectric machine, according to Faraday, and other eminent electricians, gives static as well as dynamic effects of electricity, combining quantity with intensity. These effects are ascribed to the friction of the particles of steam and water against the sides of the outlet pipes. Thus the magnetic forces may effect great physical disruptions, as well as the quiet deposition of minerals in veins and the like. M. Necker, of Geneva, long ago
†
showed that the curves of greatest magnetic intensity over the whole surface of the earth follow the bend of the different mountain ranges. Those districts most free from earthquakes are where the strata have been undisturbed, or nearly so, since their first deposition.

Systematic observations made in many regions, and afterwards correlated, appear necessary ere we can adapt these interesting isolated facts to the purposes of geological theory. This is the legitimate work of local societies.

Sir William Thomson has already called the attention of the Geological Society of Glasgow

*

to the importance of employing old bore holes for observations on underground temperature. I have to suggest that our Society embark in such inquiries in this neighbourhood. Bore holes might be taken as points of observation near the sea as well as in inland places. They might represent different varieties of rocks. An observation of the surface rainfall, as well as a little ingenuity in manipulating apparatus, might render observations of the conductive powers of the rocks practicable. Whether or no we enter on magnetic observations on the surface, I am not sure but such observations made in mines might,
inter alia,
go some way to elucidate coal-pit explosions. With the aid of those of our members practically engaged in mining, such investigation might easily be accomplished.