The Flov: of Marlle. 427 



thrown by experimental investigation. If movements 

 can be induced in rocks under known conditions, with 

 the reproduction of the structures found in deformed 

 rocks in nature, much might be learned concerning 

 not only the charcter of the movements, but also con- 

 cerning the conditions which are necessary in order 

 that the movements in question may take place. 



It is generally agreed that three chief factors con- 

 tribute to bringing about the conditions to which rocks 

 are subjected in the deeper parts of the earth's crust, 

 where folding with concomitant flowing is most 

 marked. These are : — 



1. Great pressure. 



2. High temperature. 



3. Percolating waters. 



With regard to the first factor, it must be noted 

 that mere cubic compression does not produce move- 

 ments of the nature of flowing, although it may 

 produce molecular rearrangement in the rock. A 

 differential pressure is necessary to give movement to 

 the mass. As Heim has pointed out, there is reason 

 to Ijelieve that " Umforniung ohne Bruch " takes 

 place when a rock is subjected to a pressure which, 

 vdiile greater in some directions than in others, in 

 every direction exceeds the elastic limit of the rock in 

 question. Whether all these factors, or only certain 

 of them, are actually necessary for the production of 

 rock deformation is a question which also requires 

 to he determined by experiment, for by experiment 

 the action of each can be studied separately, as well 

 as in combination with the others. 



In the paper a first contribution to such a study is 

 presented, pure Carrara marble being the rock 



