314 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



to be a very appreciable amount in the case of the greater 

 mountain-systems. On the other hand, Heim calculates that 

 the earth's diameter has not been shortened even one per cent, 

 by the processes of subsidence and mountain-folding. With 

 regard to the age of the Alps, Heim concludes that the central 

 chains are older than the outer, that the strains have wholly 

 ceased in the inner portions of the Alps, but continued along 

 the northern chains into the youngest Tertiary periods, and are 

 possibly even now in progress. 



According to Heim's theory of latent plasticity, the rocks 

 at a depth of nearly 7000 feet would be in a condition that 

 would preclude the possibility of gaping fissures. This 

 assumption is correlated with the characteristic feature in 

 Heim's geological surveys, namely, the pre-eminence of folds 

 in all possible forms, and the subordinate place assigned to 

 faults. These have proved somewhat vulnerable points of 

 attack in an otherwise classic work, and have been called in 

 question by many eminent geologists during the twenty and 

 more years that have elapsed since the publication of the 

 Meclianismus. 



Giimbel, Broegger, Stapff, Pfaff, Rothpletz, and others have 

 opposed the theory of plasticity upon various grounds. All 

 experimental attempts to reduce rocks by mere compression 

 only caused fragmentation of the material. Pfaff found that 

 many rocks might be subjected to a pressure of more than 

 20,000 atmospheres without showing any tendency to become 

 plastic. Moreover, it is not in accordance with the known 

 phenomena of volcanoes and earthquakes to assume that 

 crust-fissures cease at comparatively small depths. 



The experiments of M. Daubree and M. Favre are 

 especially noteworthy. Daubree started from the standpoint 

 that not only horizontal, but also vertical components of 

 force have acted in bending and folding the rocks of the crust. 

 His apparatus consisted of a rectangular iron frame, to contain 

 the material under pressure. The pressure was applied from 

 the side, but sometimes simultaneously from above. Instead 

 of the alternating layers of wool, cotton, and clay which had 

 been used in the experiments of Sir James Hall in Edinburgh, 

 Daubree arranged different kinds of metal plates and sheets 

 of wax mixed with clay, resin, or turpentine. By varying the 

 conditions of his experiments in respect of the intensity and 

 direction of pressure, and the kinds of material, M. Daubree 



