56 
OROGENY AND EARTH’S ROTATION 
Reasoning from the analogy of a desiccating apple it is an easy 
step to orographic wrinkling as a direct resultant of nuclear 
shrinkage. It is some such structural perspective of the Appala¬ 
chians that gave the Rogers Brothers the corner-stone of their 
theory that orographic force exerted itself horizontally; and that 
therefore the strain is tangential instead of radial. 
With the establishment of this principle of tangentially acting 
force in the formation of mountain chains crustal shortening 
seems to become a necessary corollary. The American explana¬ 
tion soon becomes widely accepted. When, in Pennsylvania, the 
Rogers calculated that in the folding of the Appalachians the crust 
was diminished by 50 miles, and when, in like manner in the Alps, 
Heim estimated that the plication reduced the breadth of that part 
' of the earth by a distance of 74 miles, Suess later felt perfectly 
secure in arguing for the general recognition of the contractional 
theory. 
Although the contractional theory, as apparently expressed by 
the phenomena attending crustal plication, may not be success¬ 
fully contested by cubical expansion facts, by the fancied proper¬ 
ties of the floating prism, by regional crust-slipping, or by local 
crust-upheaval, the recent experimental results on the tectonic ad¬ 
justment of a rotating, straticulate spheroid seem to demonstrate 
its inadequacy, and the necessity of seeking some different explan¬ 
ation. If there be other ways of bringing the results about the 
contractional theory of course goes for naught. It is now known 
that apparent crustal shortening of great extent may take place 
without regard to interior shrinkage. 
In its logical consequence the contractional theory finds curious 
expression in such figments of the imagination as the reseau pen¬ 
tagonal of Elie de Beaumont, and the tetrahedral globe of Lothian 
Green. To be sure the form known as the tetrahedron is of all 
the geometrical solids the one form which possesses the least vol¬ 
ume incompassed by a given surface area, whereas the sphere 
contains the greatest bulk within the same surface, yet the collapse 
of the latter is not necessarily any such crystallographic shape as 
that indicated by the former. 
It is shown lately that in a collapsing spheroid the initial ten¬ 
dency towards a faceted form would probably not be directly any 
such limiting shape as a four-sided solid, but some intermediate 
