DIASTROPHISM AND THE FORMATIVE PROCESSES 689 
THE INTERCHANGES BETWEEN THE TWO BASAL TYPES OF ENERGY 
Before taking up the special modes of the compressional process, 
the interchanges between the two basal types of energy need con- 
sideration. ‘The constructional and the agitative phases of energy 
are not only interchangeable but interchanges are persistently 
taking place on the surface and within the earth, and these inter- 
changes play a vital part in the process.of the earth’s self- 
compression. ‘The proper recognition of these is indispensable. 
Exchanges between thermal and mechanical energy are too 
familiar to need notice; they are a basal feature in modern industry. 
But exchanges between agitative and organizing energy, Le., 
between vibratory and revolutional energy, as such, though they 
may not differ in essence from the well-recognized interchanges, 
need a word of emphasis. Some of these changes from the agitative 
to the constructive are even more familiar than the mechanical 
changes, but interpretation has not given them the value to which 
they are entitled. We know that the grass and the trees grow, 
but we easily overlook the fact that such growth is a widespread 
and important endothermal process. It belongs to the unobtrusive 
class and does not enforce attention. The prairie fire and the 
holocaust of the forest, the complementary exothermal process, 
command our lively attention. The unobtrusiveness of endo- 
thermal action is likely to deceive us as to the balance between 
interchanges of energy in nature. The problem in any special 
case is to determine the balance between opposing actions. ‘There 
is, however, no doubt as to a real preponderance of exothermic 
action on the earth’s surface. When lavas come up from below, 
they usually undergo exothermic reactions to a greater extent than 
endothermic reactions. This in itself raises the question whether 
endothermic reactions are not preponderant in the region whence 
the lavas come. Van Hise,’ Leith,? and their associates, have 
shown by the extensive collection and study of data from the full 
tC. R. Van Hise, ‘‘A Treatise on Metamorphism,” Monogr. XLVII, U.S. Geol. 
Surv. (1904). 
2C. K. Leith and W. J. Mead, Metamorphic Geology, Henry Holt and Co. (1915). 
See particularly the chapters on ‘“‘Katamorphism” and ‘‘Anamorphism”’ in both 
works. 
