If contraction from external cooling is not the cause of the compressive forces it is necessary to seek another cause. Two years later, in 1876, Dutton attempted to provide an answer to this open question.[[91]] A review of this paper, evidently by J. D. Dana, is given in the Journal. The following explanations of Dutton’s theory and of Dana’s comments upon it are contained in a few paragraphs from this review (12, 142, 1876).
“Captain Dutton presents in this paper the views brought out in his article in volume viii of this Journal, with fuller illustrations, and adds explanations of his theory of the origin of mountains. The discussion should be read by all desiring to reach right conclusions, it presenting many arguments from physical considerations against the contraction-theory, or that of the uplifting and folding of strata through lateral pressure. There is much to be learned before any theory of mountain-making shall have a sufficient foundation in observed facts to demand full confidence, and Captain Dutton merits the thanks of geologists for the aid he has given them toward reaching right conclusions. His discussions are not free from misunderstandings of geological facts, and if they fail to be finally received it will be for this reason.
We here give in a brief form, and nearly in his own words, the principal points in his theory of mountain-making as explained in the later part of his memoir.
Accepting the proposition that there is a plastic condition of rock beneath the earth’s crust and that metamorphism is a ‘hydrothermal process,’ and believing that ‘the penetration of water to profound depths [in the earth’s crust] is a well sustained theory,’ he says that great pressure and a temperature approaching redness are essential conditions of metamorphism.... ‘The heaviest portion would sink into the lighter colloid mass underneath, protruding it laterally beneath the lighter portions where, by its lighter density, it tends to accumulate.’ He adds: ‘The resulting movements would be determined, first, by the amount of difference in the densities of the upper and lower masses, and, second, by inequalities in the thickness of the strata: the forces now become adequate to the building of mountains and the plication of strata, and their modes of operation agree with the classes of facts already set forth as the concomitants of those features.’
The views are next applied to a system of plications. ‘It has been indicated that plications occur where strata have rapidly accumulated in great volume and in elongated narrow belts; that the axes of plications are parallel to the axes of maximum deposit; and that the movements immediately followed the deposition’—the case of the Appalachians being an example in which the accumulations averaged 40,000 feet. He observes: ‘Wherever the load of sediments becomes heaviest, there they sink deepest, protruding the colloid magma beneath them to the adjoining areas, which are less heavily weighted, forming at once both synclinals and anticlinals.’
With regard to this new theory, we might reasonably question the existence of the colloid magma—a condition fundamental to 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 Dutton attempted to link to it the horizontally compressive forces which have produced folding and overthrusting. Willis in 1907[[92]] and Hayford in 1911, overlooking Dana’s objections, have attempted to make a lateral isostatic undertow the cause of all horizontal movements in the crust, adopting the mechanism of Dutton. 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; inadequate in time relation, in amount, and in expression.[[93]]
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. Dutton’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 urgency of the enormous pressures, apparently by giving rise to slow recombinations of matter into denser forms.[[94]]