700 T. C CHAMBERLIN 
In tenacious solids where impact takes place at high velocities 
and with prodigious force, as in the case of a steel target struck by 
a solid shell, there is no time for idiomolecular action, and very 
little for any form of selective or metamorphic action, and so all 
molecules are apparently caused to move over one another in a way 
that is scarcely distinguishable, if at all, from real flow. The 
slowness of the increases of stress in the interior of the earth, how- 
ever, is thought to put deep-seated diastrophism in a quite different 
category from this velocity-stress action. 
Although fluidal action is placed in a secondary order in the 
evolution of a planetesimal earth, the formation and extrusion of 
magmas play a very important function in its compression, but 
that must be left for a later article. 
