Present Problems of Geophysics. — Becker. 9 
me very possible that these fundamental ruptures of the 
globe were due to the change of figure attendant upon the 
diminution of the earth's period of rotation. Their sym- 
metrical disposition with reference to the polar axis is un- 
questionable, as well as the fact that they penetrate to great 
depths. They must be due to some tremendous force acting 
axially, which actually altered the ellipticity of the meridian, 
since these fissures could not have been formed without 
modifying the shape of the globe, and the only known dis- 
turbance of this description is the change of figure referred 
to. On the other hand, were the earth homogeneous, such 
ruptures would be expected to have as envelopes small cir- 
cles in latitude 45 degrees instead of at about latitude 70 
degrees. But since the earth is not homogeneous, this dis- 
cordance does not invalidate the suggestion. 
Be this as it may, upheavals, subsidences and attendant 
contractions have been in progress throughout the whole of 
historical geology or the period within which fossils afford 
a guide to the succession of strata. The so-called contrac- 
tional theory has shown itself wholly inadequate to account 
for the amount of deformation traceable in the rocks of the 
globe, nor has the extravasation of igneous rock been suffi- 
cient to account for the phenomena. To me the earth appears 
to be a somewhat imperfect heat engine in which the escape 
of thermal energ}^ is attended by the conversion of a part 
of the supply into the vast amount of molar energv mani- 
fested in the upthrust and crumpling of the continents. The 
subject will probably turn out to be accessible mathematical- 
ly after certain experimental determinations have been made 
and I shall return to it presently. 
Orogeny or mountain building is a mere detail of the 
more general subject of upheaval and subsidence, but it ex- 
hibits problems of great complexity both from the experi- 
mental and from the theoretical points of view. There is no 
question that unit strains are often reached or even sur- 
passed in contorted strata and in belts of slate, but the theo- 
ries of elasticity and plasticity as yet developed are inade- 
quate to deal with these strains in complex cases. An in- 
vestigation on finite elastic and plastic strain is now under 
way in my laboratory and has made gratifying progress thus 
