72 Intelligence and Miscellaneous Articles, 



" magma " — the former less dense and highly silicated, the latter 

 basic and rich in magnetic iron-ore. This view was in accordance 

 with those of Durocher, Prestwich, Eisher, and many other geolo- 

 gists. The composition of this inner magma, and the condition in 

 which the magnetic iron-ore exists were then discussed, and it was 

 shown that it probably exists under the form of numerous small 

 crystals with a polar arrangement. Each little crystal being itself 

 a magnet and having crystallized out from the magma while this 

 latter was in a viscous condition, the crystalline grains would 

 necessarily assume a polar arrangement which would be one of 

 equilibrium. Basalt might be taken as the typical rock of this 

 magma. 



The thickness and depth of the magnetic magma beneath the 

 surface of the globe were then discussed, and while admitting that 

 it was impossible to come to any close determination on these points 

 owing to our ignorance of the relative effects of increasing tempera- 

 ture and pressure, it was assumed tentatively that the outer 

 surface of the effective magnetic magma might be at an average 

 depth of about 100 miles, and the thickness about 25 or 30 miles. 

 The proportion of magnetic iron-ore in basaltic rocks was then 

 considered, and it was shown that an average of 10 to 15 per cent, 

 would express these proportions ; and assuming similar proportions 

 to exist in the earth s magnetic magma, we should then have an 

 effective terrestrial magnet of from 2| to 3 miles in thickness. 

 The thickness is, however, probably much greater. 



Instances of polarity in basaltic masses at various localities were 

 adduced in order to illustrate the possibility of polarity in the 

 internal mass. 



The subject of the polarity of the globe was then discussed, and 

 it was pointed out how the position of the so-called " magnetic 

 poles " leads to the inference that they are in some way dependent 

 upon the position of the terrestrial poles. 



The author regarded the double so-called " poles " as merely foci 

 due to protuberances of the magnetic magma into the exterior non- 

 magnetic magma, and that there was really only a single magnetic 

 pole in each hemisphere, embracing the whole region round the 

 terrestrial pole and the stronger and weaker magnetic foci, and 

 roughly included within the latitude of 70° within the northern 

 hemisphere. 



It was pointed out that the poles of a bar-magnet embrace a 

 comparatively large area of its surface, and hence a natural terres- 

 trial magnet of the size here hypothecated may be inferred to 

 embrace a proportionably large tract for its poles. 



In reference to the question why the magnetic poles are situated 

 near those of the earth itself, this phenomenon seemed to be con- 

 nected with the original consolidation of the crust of the globe, and 

 the formation of its internal magmas. 



It was pointed out that, in the case of the magnetic magma the 

 process of crystallization and the polar arrangement of the particles 

 of magnetic iron-ore would proceed in a radial direction. The 



