166 Barrell — Grotvth of Knowledge of Earth Structure. 



the theory — and his evidence that water penetrates to profound 

 depths in the earth's crust sufficient to make hydrous rocks. 

 "We might ask for evidence that the rocks beneath the Cretaceous 

 and Tertiary, and other underlying strata of the Uintahs, were 

 in such a colloid state, and this so near the surface, that the 

 ' beds subsided by their gross weight as rapidly as they grew. ' 



Again, he says that the movements of mountain-making 

 'immediately followed the deposition.' 'Immediately' sounds 

 quick to one who appreciates the slowness of geological changes. 

 The Carboniferous age was very long; and somewhere in that 

 part of geological time, either before the age had fully ended, 

 or some time after its close, the epoch of catastrophe began." 



We see foreshadowed In this paper the theory of 

 isostasy, or condition of vertical equilibrium in the crust 

 which Dutton published in 1889. This theory has borne 

 remarkable fruit, but Button attempted to link to it the 

 horizontally compressive forces which have produced 

 folding and overthrusting. "Willis in 1907 15 and Hayford 

 in 1911, overlooking Dana's objections, have attempted 

 to make a lateral isostatic undertow the cause of all hori- 

 zontal movements in the crust, adopting the mechanism 

 of Button. The present writer, although accepting the 

 principle of isostasy as an explanation of broad vertical 

 movements, has published papers which go to show the 

 inadequacy of this hypothesis of lateral pressure ; inade- 

 quate in time relation, in amount, and in expression. 16 



In 1903 it was determined by several physicists that 

 the materials of the earth's crust were radioactive and 

 must' generate throughout geologic time a quantity of 

 heat which perhaps equalled that lost by radiation into 

 space. By 1907 this had become demonstrated. The 

 remarkable conclusion had been reached that the earth, 

 although losing heat, is not a cooling globe. But- 

 ton's contentions against mountain growth through 

 external cooling and contraction were thus unexpectedly, 

 through a wholly new branch of knowledge, demonstrated 

 to be true. 



Nevertheless, all students of orogeny are agreed that 

 profound compressive forces have been the chief agents 

 in developing mountain structures. Chamberlin was 

 the first to arrive at the idea that the shrinkage may 

 originate in the deeper portions of the earth under the 



15 B. Willis, Research in China, vol. 2, 1907. 



16 Joseph Barrell, Science, 39, 259, 260, 1909; Jour. Geol., 22, 672-683, 

 1914. 



