220 F. B. TAYLOR ORIGIN OF THE EARTH's PLAN 



mountain ranges produced by the Tertiar}^ crustal movements are found 

 mainly in middle and low latitudes — that is, along the lower margins of 

 the crustal sheets. 



Eelation of the Tertiary crustal Movements to the Earth's 



Plan 



Enough has been said in the preceding pages to show how the present 

 plan of the earth has been affected by the Tertiary crustal movements. 

 All the continents excepting Indo-Africa were affected and modified 

 by them. As Suess observes, all the older parts of the continents were 

 subjected to folding before the Tertiary, and yet it is certainly true that 

 the Tertiary movements dominate largely in the earth's present plan and 

 have given all the continents the larger part of their present outlines, 

 excepting Indo-Africa. 



One of the most remarkable things in the earth's plan is the fact 

 that so much land appears to be clustered around the north pole and so 

 little around the south pole. The northern hemisphere is largely conti- 

 nental, while the southern is mainly oceanic. In the northern hemi- 

 sphere, however, Greenland is the only large remnant of the original 

 north polar continent and most of the polar region is open sea, much of 

 it deep, while in the southern the pole and the polar regions generally 

 are occupied by the Antarctic continent, which is many times larger than 

 Greenland. These peculiarities have not been explained, but if flatten- 

 ing of the poles with crustal dispersion characterized the Tertiary de- 

 formation as described above, then a simple explanation seems available. 



Suppose the earth to have been originally a perfect sphere, and then 

 to have been subjected to polar flattening, like that described above and 

 suggested by Suess himself in one of his later works. This would change 

 the earth to an oblate spheroid. The polar flattening, with a tendency 

 to crustal dispersion, may be supposed to affect both poles at once and at 

 first equally. 



Now the first pole to undergo a crustal movement toward lower lati- 

 tudes on a large scale would manifestly cause a slight shifting of the 

 earth's center of gravity toward the other pole. Suppose the first large 

 movement to have been from the north pole, then the earth's center of 

 gravity would be shifted slightly toward the south pole. This would 

 leave the remaining north polar lands under slightly greater strain than 

 before, while the strain tending to dispersion of south polar lands would 

 be proportionally diminished. 



Such a change would, of course, increase the chances of further move- 



