228 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1924 



of their increasing density from the periphery to the center. Tlie 

 zone next to the surface is formed of light rocks such as granite, 

 rich in silica, oxygen, and aluminium ; it is the salique zone or the sal 

 (Si, Al) of Edward Suess. Lower, silica, oxj^gen, and aluminium 

 diminish, while calcium, iron, and magnesia increase; it is the zone 

 simique or the sima (Si, Mg) of Edw^ard Suess. Lower still, there 

 is little but iron, with some other metals, such as nickel; Edward 

 Suess called this zone niflque or the nife (Ni, Fe). The probability 

 is that the series of the mingling of the elements may be continuous, 

 and that there may be no precise demarcation between sal and sima^ 

 between sima and nife. The same holds for the physical conditions. 

 Under the solid lithosphere there is the liquid pyrosphere; under 

 the latter, what is the physical condition of the deep interior which 

 becomes little by little nifique in its composition? Is it a solid? Is 

 it a gas? We do not know, and we content ourselves with calling 

 this interior the harysphcre. The probability is that there may be 

 a continuous gradation from the solid of the lithosphere to the 

 liquid of the pyrosphere, and also from the liquid of the pyro- 

 sphere to the unknown physical condition which is that of the bary- 

 sphere. It is not, however, absolutely impossible that there may be 

 some discontinuities, especially in the series of the physical condi- 

 tions ; but, if such, they elude us, of course, at every conjecture. 



To uproot the continents and render them mobile, Wegener sup- 

 poses the existence of such discontinuities ; he supposes that the sep- 

 aration of the sal and sima is clearly marked. The sal forms the 

 continents ; they are entirely solid. The sima under them is entirely 

 liquid, without the viscous transition between liquid and solid ; under 

 the oceans there is only siTua, at first a very thin pellicle of solidi- 

 fied sima, then, under that, the general bath of molten siTna. 

 Wegener admits that the sal, of which the continents are formed, is 

 a solid having a mean density 2.8; he admits, on the other hand, 

 that the liquid sima has a mean density of 2.9. A piece of continent, 

 a fragment of sal, floating on a simique bath, will be deeply sub- 

 merged in it, after the manner of mountains of ice which float on 

 the sea, whose submerged depth is very much greater than their visible 

 height; for the fragment of continent, the submerged depth will be 

 about nineteen times the emerged height. As there is a difference 

 of nearly 5 kilometers between the mean distance to the center of 

 the earth of the continental domain and the submarine domain con- 

 stituted by the bottom of the oceans, it is necessary, says Wegener, 

 that the continents be submerged some 95 kilometers in the liquid 

 simxi. 



Can you conceive of this strange earth? Around her a spherical 

 liquid envelope, formed of lava, which if it became solidified would 

 be analogous to basalt ; this lava is not only liquid, but very mobile, 



I 



