112 R. M. Deeley — Mountain Building. 



resulted only in the bulging up or general elevation of the great 

 central massifs, and in diminishing the width of the entire Alpine 

 area. Many years ago Professor Heim was of opinion that if all the 

 Alpine folds were smoothed out and the strata regained their original 

 position, they would necessarily extend over a much wider area; 

 the two points Zurich and Como, for example, would be further 

 apart than they are at present by some 120 to 150 kilometres. But 

 this estimate he thinks is now much under the mark ; according to 

 him, the Alpine area before compression took place was a flat land 

 measuring probably 600 to 1,200 kilometres across. Instead of this 

 broad low-lying tract, we have now a lofty mountain chain averaging 

 no more than 150 kilometres in width." He accounts for the com- 

 pression by adopting the theory that "The movements referred to 

 are doubtless due to the wrinkling of the earth's crust over the 

 slowly cooling and contracting material ". 



The above quotations have been made for the purpose of showing 

 what may be considered to be the attitude of very many geologists 

 at the present day. However, the theories he advocates he did not 

 originate, but they certainly appeared to him to be sufficiently well 

 established to admit of their being placed before the public as sound. 



Many physicists who have carefully studied this theory of com- 

 pression by cooling are quite satisfied that it is not capable of 

 accounting for the amount of compression required. 0. Fisher, for 

 example, maintains that secular contraction of a solid globe through 

 mere cooling will not account for the observed phenomena. The idea 

 is that the already cooled surface of the earth was thrown into folds 

 as the hotter interior cooled. We must assume, for instance, that 

 during the formation of the Alps the compression may have amounted 

 to 1,200 — 150 kilometres, or 1,050 kilometres. To effect this, even 

 if the whole of the crumpling were concentrated in the Swiss Alpine 

 region, the earth must have decreased in diameter by about 334 

 kilometres. Indeed, the contraction that is required in the diameter- 

 of the earth is very much greater than can possibly be allowed. 



Thrust planes have also been regarded as proof of compression.* 

 J. Geikie remarks : " But notable as these rock-movements are, 

 they cannot compare in extent to the similar translations which have 

 been recognized in Scandinavia, where in one particular case a massive 

 sheet, many thousand feet thick, is believed by some geologists to 

 have been driven from west to east, for a distance apparently of 

 80 miles or thereabouts." It is unfortunate that these faults should 

 have been called " thrust planes ". It would be impossible to thrust 

 a sheet of rock over the surface beneath if the proportions of thickness 

 to distance were anything like those mentioned. A force applied to 

 one end of such a rock sheet would merely buckle it up for a short 

 distance. "Gliding plane " would be better than "thrust plane" 

 as a name for such phenomena. 



In view of the considerations that have been mentioned, it would 

 be well to consider whether the folding, etc., that is so often exhibited 

 in mountain chains may not be the result of other agencies. 



1 Ibid., p. 173. 



