Dr, E. Naumann—Magnetism and Earth Structure. 489 
‘but the magnetic property is developed after being exposed to the 
atmosphere for some time. 
In the above-mentioned memoir I have endeavoured to prove that 
the so-called “rock magnetism” does not produce the distortion of 
magnetic curves, and J here quote one example to show how insigni- 
ficant these local disturbances are. The long chain of mountains, 
Katschanar-Blagodat-Wissakaja Gora of the Ural, consist chiefly of 
magnetic iron ore, and although the compass is strongly affected in 
the immediate neighbourhood of the ore in the quarries, yet the chain 
produces no remarkable distortion in the system of magnetic curves. 
Other examples might be given to show that “rock magnetism” is 
a secondary phenomenon confined to the very surface of masses, and 
not a property of the masses themselves. Moreover, the surfaces of 
rocks which exhibit magnetic properties, generally present a con- 
siderable number of irregularly distributed poles. 
The connexion between magnetic and structural phenomena was 
foreseen by several distinguished observers. It was on the 26th of 
May, 1849, that Kreil read his paper “‘ On the Influence of the Alps 
on the Reactions of the Magnetic Force of the Harth.”! He was 
not clear about the tectonic relations, but knew with certainty 
that some connexion existed between magnetic phenomena and the 
internal condition of the earth’s crust, and that the cause of mountain 
ranges had considerable influence on the direction of the magnetic 
curves. 
At a still earlier date Locke communicated his paper to the 
American Philos. Soc. of Philadelphia? In it, many interesting 
observations were made which might have been followed with 
advantage, but unfortunately his work, like that of many others, 
was forgotten. He surveyed magnetic profiles, and plotted inclination 
curves having distances as abscisse and “magnetic dips” as 
ordinates. The curve for the line passing over the horizontally 
stratified rocks of the West, through Kentucky and Ohio, and along 
the Mississippi, shows generally a very gradual rise until it crosses 
eruptive rocks between Baltimore and New York, where it exhibits 
a rise and fall ‘like the contour of primitive or igneous mountains.” 
(See Plate XV. Fig. 1.) ° 
Many extensive surveys have been made since Humboldt and Gauss 
brought the subject into prominence, but there have been few 
observers who were not somewhat embarrassed by the mathematical 
theory of Gauss, and nearly all have considered the irregularities 
in magnetic charts as something accidental, anomalous and vexatious. 
The recent activity in magnetic surveying is very gratifying, but 
many observers still use the old methods, although they are capable 
of considerable improvement. 
The rate of progress could be further accelerated by establishing 
' Denkschriften der Kaiserlichen Akademie der Wissenschaften. Mathem. natur- 
wissench. Klasse. Bd. I. Wien, 1850. 
2 Locke, Observations of the Magnetical Force in several parts of the United 
States. Trans, Am. Phil. Soc. of Philadelphia, vol. ix. 1846, p. 283. 
* The Plates illustrating Dr. E. Naumann’s paper will accompany Part II. in 
December Number Grou. Mac.—Epir. 
