340 J. D. Dana on the Plan of Development 
The organizing agencies in the sphere are— 
1. Chemical combination and crystallization. 
2. Heat, in vaporization, fusion, and expansion, with the cor- 
relate force of contraction which has been in increasing action 
from the time the globe began to be a cooling globe. . 
. The external physical agencies, preéminently water and 
the atmosphere, chiseling and moulding the surface. 
4. The superadded agency of life. 
ear or wrinkle the crust, as the same cause, contraction, WriN- 
les a drying apple. The large rind is more than sufficient for 
the contracted sphere; and the drawing downward of some parts 
