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the sides must lose as much as the sediments gain, and therefore must contract and make room for the lateral expansion, and therefore there would be no folding and no elevation. I do not see any escape from this objection.
Thus it seems that Reade's theory cannot be accepted as a substitute. Is there any other?
II. DUTTON'S ISOSTATIC THEORY.[1]
Dutton's discussion of isostasy is admirable, but his application of it to the origin of mountains is weak. The outline is as follows:
Suppose a bold coast line, powerful erosion and abundant sedimentation. The coast rises by unloading and the marginal sea-bottom sinks by loading. Now if isostasy is perfect, there will be no tendency to mountain formation. But suppose a piling up of sediments, but—on account of earth rigidity—without immediate compensatory sinking, and a cutting down of coast land without compensatory rising. Then there would be an isostatic slope toward the land. And the accumulated and softened sediments would slide landward, crumpling the strata and swelling them up into a mountain range.
The fatal objection to this view is that complete isostasy is necessary to renew the conditions of continued sedimentation and therefore to make thick sediments, otherwise the sediments quickly rise to sea-level and stop the process of sedimentation at that place. But it is precisely a want of complete isostasy which is necessary to make an isostatic slope landward. Dutton refers to Herschel as having suggested a similar cause of strata crumpling and slaty cleavage[2]; but the principles involved in the two cases are almost exactly opposite. Herschel supposes sediments to slide down steep natural slopes of sea-bottoms and therefore seaward. Dutton supposed sediments to slide up natural, though down isostatic slopes, landward. Herschel's is a theory of strata-