4:66 Adams <& Coker — Investigation into the Flow of Rocks. 



has often been a marked transfer or " flow " of material from 

 one place to another within the fold. 



While, however, these facts are undisputed, the precise 

 nature of this folding and flowing has been a subject concern- 

 ing which there has been much discussion and a wide diver- 

 gence of opinion. 



Some authorities — among whom Heim,* whose work in the 

 Alps must command the admiration of all, may be mentioned 

 — have held that while in the upper portions of the earth's 

 crust, rocks when submitted to pressure will break, giving rise 

 to faults and overthrusts — the same rocks in the deeper por- 

 tions of the earth's crust are unable to break up in this way, 

 owing to the great weight of the superincumbent strata. The 

 lines of fracture they hold in this case become smaller and 

 greatly increase in number, the various minerals constituting 

 the rock thus breaking down into grains, which, however, 

 move around and past one another, the adjacent grains always 

 remaining within the sphere of mutual cohesion. The struc- 

 ture of the rock thus becomes cataclastic ; but the rock mass, 

 while acting as a plastic body and flowing in the direction of 

 least resistance, maintains its coherence while altering its shape. 



Now according to Spring, f the property known as regela- 

 tion is really due to a power which fragments of bodies have 

 of uniting if brought within the range of the molecular forces, 

 a property which, although possessed in a marked manner by 

 ice, is also, as he has experimentally demonstrated, exhibited 

 by many other bodies and would probably be displayed by all 

 if the required conditions could be attained. The " flow of 

 rocks " would, therefore, according to Heim's view, be a mani- 

 festation of regelation on an enormous scale. 



Other writers on this subject have maintained that rocks are 

 absolutely destitute of plasticity in any proper sense of the 

 term. PfaffJ has even held that in the depths of the earth 

 great pressure will tend rather to prevent molecular move- 

 ment and thus keep the rocks rigid. Those holding such 

 views attribute the deformation of rocks either to crushing 

 with subsequent recementation of the fragments by mineral 

 matter deposited from percolating waters as the movements 

 proceed or after they are completed, § or to a continuous 

 process of solution and redeposition of the minerals which 



* Der Mechanismus der Gebirgsbildung, p. 31, 1878 ; see also Van Hise, C. 

 E. , Metamorphism of Eocks and Eock Flowage, Bull. Geol. Soc. of America, 

 vol. ix, 1898. 



f Eecherches sur la propriete que possedent les corps de se souder sous 

 Taction de la pression ; Eevue Universelle des Mines, 1880. 



% Der Mechanismus der Gebirgsbildung, pp. 19-21. 



§ Stapff, Zur Mechanik der Schichtenfaltungen, Neues Jahrbuch fur 

 Mineralogie, 1879, p. 792 ; Eeyer, Theoretische Geologie, p. 443. 



