REPORT OF THE DIRECTOR 1920-21 135 



faults or folds are the result of the riding or dragging of the upper 

 layers by the underlying materials." Suess pictured to himself the 

 mountain chains as the crumpled edges of flat-based earth scales, a 

 view that apparently finds support not only in the grand arrangement 

 principally of the Asiatic ranges but also in the fact that the angles 

 of the fold faults or thrust planes observed in connection with these 

 folds, notably the Himalayas, are very flat (see Middlemiss, 1919, 

 p. 565, also Quirke 1920). 



Both in America and in Europe one has recognized the relatively 

 deep-seated origin of folding. Gilbert had pointed already to 

 that of the Appalachian folding, as revealed by the great erosion, 

 and Dutton (1874, p. 163) had early urged that the surficial cooling 

 of the globe could not account for the magnitude and the nature and 

 distribution of the mountain folds. Under the leadership of 

 Chamberlin the conclusion has been reached that the shrinkage of the 

 earth originates in the deeper portions of the earth and that its 

 controlling cause is the enormous pressure which induces slow 

 recombinations and recrystallizations of matter into denser form. 

 One has further concluded that the oceans are the principal sites of 

 this condensation deep within the earth; and further that these 

 condensations create the irresistible horizontal compressive forces. 

 Under the influence of the forces created by the condensation, 

 yielding by massive flowage takes place in the zone of rock flowage, 

 which underlies the zone of fracture. The foliated structures and 

 crystalline textures of the Precambrian rocks testify to the fact 

 that they have been in the zone and under the influence of this 

 flowage, through granulation and recrystallization. Experiments by 

 Tammann (1903) on the rate of flowing of crystallized substances 

 have shown that the flowing is not dependent upon a previous 

 melting, but that the plasticity, the reciprocal interior friction, 

 is a property peculiar to crystals and that it rapidly grows with 

 the deforming force and increasing temperature and reaches large 

 figures near the fusion curve. Tammann's investigations reveal 

 complicated processes of crystallization and changes of volume 

 that may have produced contraction and expansion at the same time 

 at different places, as well as a general contraction or expansion. 

 Such results lead to the view of the possibility of massive convection 

 currents or " Unterstromungen," a hypothesis especially developed 

 by Ampferer (1906), 1 and they also give a clue to a possible explana- 



1 Ampferer's hypothesis is distinct from that advanced by Willis (1907) and 

 Hayford (191 1), who adopting the mechanism of Dutton, have attempted to 

 make a lateral isostatic undertow — the cause of all horizontal movements in 

 the crust. Barrell (1909, 1914, p. 166) has rejected this hypothesis as inadequate. 



