The Poiver of Gravity. 
513 
graded by the wasting forces of water, ice, and wind. Concur¬ 
rent with these movements is deep-seated flowage. As a result 
of these movements it is possible that the continents may grow. 
The remote cause to which continent-making, differential sub-, 
sidence, mountain-making and attendant phenomena, epigene 
transfer, vulcanism, and deep-seated compensatory flow, are due, 
is the force of gravity persistently working upon a plastic con¬ 
tracting mass; and therefore the center of gravity of the vari¬ 
ous masses moved, is nearer the center of the earth as a result 
of the movements. 1 
Furthermore gravity is ever working toward isostatic equilib¬ 
rium, but the rigidity of the rocks ever prevents its perfect ac¬ 
complishment. The limit of excess or deficiency maintained by the 
strength of the rocks in any district is measured by the elastic limit 
of the rocks deformed, under the varying conditions of deformation. 
Some of these varying conditions are the magnitudes of the 
masses, the character of the rocks, the temperature of the rocks, 
the water content of the rocks, and the rapidity of the deforma¬ 
tion. The greater the length and breadth of the mass moved, 
the less the thickness of the excess or deficiency which may be 
1 This generalization is in accord with that which Prevost urged many 
years ago, as is shown by the following quotation from the Bull, of the 
Geol. Soc. of France, Vol. XI, 1840, p. 186: 
“ 1. Que le relief de la surface du sol est le resultat de grands affaise- 
ments successifs, qui, par contre-coup, et d’une maniere secondaire, ont 
pu occasioner accidentellement des elevations absolues, des pressions lat¬ 
erals, des ploiements, des plissements, des ruptures, des tassements, 
des failles, etc.; mais que rien n’autorise a croire que ces divers accidents 
ont ete produits par une cause agissant sous les sol, c’est-a-dire, par une 
force soulevante;” 
“2. Que les dislocations du sol sont des effets complexes de retrait, de 
contraction, de plissement et de chute;” 
“3. Que les matieres ignees (granites, porphyres, trachytes, basaltes, 
lavas,) loin d’avoir souleve et rompu le sol pour s’eschapper, ont seule- 
ment profite des solutions de continuity qui leur ont ete offertes par le re¬ 
trait et les ruptures, pour sortir, suinter et s’epancher audehors.” 
As proof of this paper is passing through my hands, through the gen¬ 
erous courtesy of Major J. W. Powell I am in receipt, in advance of publi¬ 
cation, of his manuscript on An Hypothesis to Account for Earth Move¬ 
ments (to be published in the Jan.-Feb. number of the Journal of Geol. 
33 
