458 EMERSON— RECURRENT TETRAHEDRAL DEFORMATIONS. 



poles?" This would rule out pendulations of the north pole into 

 the present southern hemisphere and back again, but need not be 

 called a mathematical proof that the pole may not have moved in 

 several stages i5°-2o° from a point north of Behring's Straits to 

 its present position. But even this is not absolutely necessary be- 

 cause we may make the assumption that the Pleistocene tetrahedral 

 deformation was so irregular that the southern half of one lobe 

 (Africa) was so abnormally raised that the Alpine chains flowed 

 north to partly submerge Europe and when the collapse came the 

 sinkings caused the three-lobed Mediterranean and the Black Sea, 

 as the China seas were formed. 



In accordance with the idea of multiple working hypotheses we 

 may examine and compare the other current theories concerning the 

 genesis of continents, and see if any reason exists why the tetra- 

 hedral tendency may not coexist with all other agencies of defor- 

 mation and sometimes partially control the result. 



See postulates a thrust from the suboceanic area against or be- 

 neath the continental areas, getting the force from oceanic leakage 

 by which abundant sea water penetrating the subcrusted lava froths 

 it so that, expanding, it is thrust beneath the coastal border and 

 raises it in mountain chains. It is difficult to understand why, if 

 the sea bottom cracks, and water penetrates to the deep-seated lavas, 

 the expansive force should not relieve itself through the fissured 

 area whence the waters come, rather than propagate itself Inany 

 hundred miles beneath coastal areas and form inland mountain 

 chains. 



From the deflection of the pendulum at the various stations of 

 observation in the United States Heyford concludes that " isostatic 

 compensation " exists in a superficial earth shell about seventy-one 

 miles thick, so that a short suboceanic vertical section is of equal 

 weight with a long continental one of the same base. If unloading 

 by erosion takes place, the unloaded area will expand because de- 

 crease of pressure favors those chemical and solution changes which 

 increase bulk, and vice versa the loaded area will contract because 

 increase of pressure will tend to favor those chemical and solution 



