230 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1924 



tion of gravity in mountainous countries by noting that in the 

 mountains and under them the parts of the lithosphere nearest to 

 the surface, and hence the lightest, are folded and heaped on them- 

 selves and thus they have driven back toward the depths the denser 

 lower zones. One can also contend that the differences of gravity 

 are original; that the lithosphere is not and never has been homo- 

 geneous; that the oceans installed themselves, from the beginning, 

 over the densest regions, which correspond to the depressions of the 

 surface ; that the continents are the less dense regions ; and that this 

 primitive distribution of relief has hardly changed up t6 our time. 

 The consideration of the inequalities of gravity does not solve, then, 

 the question of whether the continents can drift widely or whether 

 they have been anchored for a long while ; since on the earth, which 

 had just cooled, the seas were formed and circumscribed. 



In the theory of Wegener as the author presents it to us, there are 

 numerous and strong improbabilities. The whole is seductive ; many 

 of the details are startling. I do not speak of the fundamental con- 

 ception, little probable, little satisfying, of the existence of the 

 physical and chemical discontinuities in the interior of the earth. 

 But who could believe, for example, in the formation of moimtain 

 chains by the reaction of the liquid sivia on the advancing continent ? 

 If the sima is capable of opposing such a resistance to the movement 

 of the floating mass, how is it that this mass is not held by the si7na 

 and how can it move ? In the hypothesis of mobility, what becomes 

 of the debris of the solid simique pellicle which forms the bottom of 

 the ocean ? Should it not accumulate in a thick fold of dark heavy 

 rocks under the prow of the great ship ? But nothing resembling it 

 appears. How can the deep foldings of the solid continental sal, 

 under the thrust of the liquid sima, transform itself in rising toward 

 the surface and form these folds and beds that we see in our moun- 

 tains and which suggest the idea of superficial wrinkles much more 

 than that of a very deep seated disturbance propagated in a vertical 



direction. 



Supposing that one could accept Wegener's orogenic hypothesis 

 for the Cordilleras of western America, or south Africa, or eastern 

 Australia, it would be necessary to find another to explain the Alps, 

 the Apenines, the Caucasus, the great chains of Central Asia. This 

 is indeed what Wegener tries to do; but who is the tectonician who 

 would consent to accepting two entirely different orogeneses, one 

 for the Andean pile and those resembling it, another for the im- 

 mense transverse chains which are the highest summits of our world 

 and which have replaced the ancient Tethys? How believe that 

 under the oceans the basalt magma may have a density of 2.9 and that 

 it may still have the same density under the continents at a very 

 much greater depth, 95 kilometers greater ? 



