394 of the Grand Outline Features of the Earth. 
formity between the facts and the necessary effects of this cause. 
Mr. Darwin adopting essentially the same view in his remarks 
on the parallel relation of the planes of cleavage in western 
South America to the axis of the Andes range, explains the uni- 
formity by supposing the mass to have been subjected to tension 
unequal in different planes, arising from the elevation of the 
mountains.* Mr. Sedgwick in his valuable memoir “On the 
Structure of Large Mineral Masses,” (1835,) also appeals to ten- 
sion as the cause supposes that this tension may arise from 
they must have been lines of equal cooling, and consequently 
lines of equal tension. This cause would then cooperate wi 
the electrical, and might aid in producing the general uniformity 
of trend, which could not proceed from contraction alone. Act- 
ing during the period of early cooling, its effects should therefore 
have been universal: and through subsequent ages, the cooling of 
e cause, liable to those modifications that isodynamic 
lines have undergone. But a perfect correspondence in the sur 
grand result for geology if the science should settle this debat 
point. ‘The coincidence of the magnetic curves with the trends 
w Ho 
+ Trans. Geol , London, ii Ser., ii , March, 
dal movements in the fluids during incipient cooling migh — 
n, transverse to the line of motio nid a gradual change in the oblateness 
