74 PRESIDENTS ADDRESS—SECTION C. 
prising less than a geological period ; nevertheless, the elevation is 
often less rapid than the rate of river erosion. 
5. Folding does not go on pari passu with sedimentation, but 
the rocks in the geosynclinal remain uncontorted until the for- 
mation of the synclinorium has commenced. 
6. The formation of the synclinorium is usually followed by 
subsidence of short duration, which is again followed by a regional 
uplift with local plications of the newly deposited beds, generally 
along one side only of the synclinorium. 
7. Superficial rocks have been folded as well as deep-seated 
ones, while flexures like those of the Jura and Uinta Mountains 
are also local uprisings of the surface. Consequently, mountain 
ranges of the Alpine type are not the cores of broad plateaux 
exposed by denudation, as taught by Montlosier, but are uprisings 
from the surface, as taught by Von Buch, and may or may not 
be accompanied by regional uplifts. 
8. Folding only takes place where the sediments are thick ; 
nevertheless, very thick deposits are not in every case folded, 
showing that great sedimentation does not cause plication 
directly. 
9. The forces which produce mountain ranges are only a modi- 
fication of those which produce regional uplifts. 
STATE OF THE INTERIOR OF THE EARTH. 
It now becomes necessary to ascertain what is known about 
the condition of the interior of the earth, on the surface of 
which these movements take place ; for it is evident that, before 
we can approach with confidence the question of causes, we must 
know not only the facts connected with the oscillations of the 
surface, but also what assumptions are allowable about the state 
of the interior. Fortunately, this problem has been much simpli- 
fied by the mathematical investigations of Sir W. Thomson, 
Professor G. H. Darwin, and the Rev. O. Fisher, so that a short 
history of opinion on the subject will place any one in a position 
to judge for himself. 
Leibnitz, in 1683, started the theory of an incandescent globe, 
the interior of which was fluid, and re-acted on the cooled surface ; 
and he was followed by Descartes, Bufton, Hutton, and Dolomieu. 
But, in 1681, Bishop Burnet had maintained the opposite opinion, 
viz., that the earth is a solid, cold, inert mass, the surface of . 
which was at first dissolved in a watery menstruum, and had 
gradually dried, the surplus water having been drawn off into 
caverns in the interior,—a doctrine which was supported by 
Woodward, Werner, De Luc, Pallas, De Saussure, and others. 
The discussion was long and even personal, but the bishop’s side 
so completely gained the day that, in 1811, Pinkerton said that 
“the doctrine of a central heat seems to be universally aban- 
