Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/36

12 simplicity of its basic principle and the multiplicity of its applications still give it a strong hold. Nevertheless, there can be no doubt that the contraction theory stands in direct contradiction to all the recent conclusions of geophysics, and that the course of geological research tends to deviate more and more from it.

The already difficult explanation of the mountain chains by reason of a shrinkage of the earth has been made to appear even more unsatisfactory by the discovery of the imbricated sheet folding or over-thrusting in the Alps. This new conception of the structure of the Alps and of numerous other mountain ranges, developed by the work of Bertrand, Schardt, Lugeon and others, involves far greater amounts of contraction than do previous suppositions. Whilst Heim, according to the latter, calculated a shortening of one-half for the Alps, he finds to-day, on the basis of the present generally accepted sheet-folding structure, a shortening to one-quarter or one-eighth.

Since the present breadth amounts to about 150 km., there would thus have been thrust together a portion of the crust of about 600 to 1200 km. (5 to 10 degrees of latitude). Any attempt to deduce such a decrease in diameter from a lowering of the temperature of the earth’s interior is bound to fail. E. Kayser remarks that a contraction of 1200 km. constitutes only 3 per cent. of the circumference of the earth, so that the radius must also be decreased about 3 per cent. These figures are significant only when the temperatures to which they correspond are calculated. On the basis of the average value of the four linear coefficients of expansion of nickel (0.000013), iron (0.000012), calcite (0.000015) and quartz (0.000010) giving 0.0000125, a loss of heat of about 2400° C.