522 T. C. CHAMBERLIN 
internal stresses. But in elastic bodies a specific amount of stress 
is prerequisite. The working tenets for elastic bodies must take 
account of this. There is a real plasticity and a quasi-plasticity. 
The planetesimal hypothesis therefore lends its weightier pre- 
sumptions to the belief that the earth, or at least its outer mass to 
great depths, is essentially an aggregate of crystals and derives from 
them, in a composite form, a measure of their solid elastic properties. 
The working tenets of this hypothesis are thus normally as dis- 
tinctly elastico-rigid as are those of the gaseous genus of cos- 
mogonies normally of the viscous type. 
It has seemed worth while, therefore, to shape some of the 
studies in hand so that they will contribute, if they may, to the 
evolution of the working conceptions appropriate to masses of 
crystals of earth-dimensions under earth-conditions. Such articles 
may equally serve the more specitic purposes implied by their titles. 
The discussions now in mind have grown out of studies on formative 
and on diastrophic processes. Time has changed the order of 
primacy from the formative of the early ages to the deformative of 
the later ages, at least it so seems to the student of present problems. 
We therefore chose the general title “Dia trophism and _ the 
Formative Processes”? as a thread by which to preserve the sem- 
blance of continuity of purpose through the series of articles that 
may themselves seem more or less heterogeneous. The writer of 
this word of introduction will not be the sole contributor. 
