Whatever be the connection between the deposition and

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the subsequent upheaval, the element of great depth of accumulation seems a necessary condition and must evidently enter as a factor into the Physical Processes involved.  The mountain range can only arise where the geosyncline is deeply filled by long ages of sedimentation.

Dana’s description of the events attending mountain building is impressive: 

“A mountain range of the common type, like that to which the Appalachians belong, is made out of the sedimentary formations of a long preceding era; beds that were laid down conformably, and in succession, until they had reached the needed thickness; beds spreading over a region tens of thousands of square miles in area.  The region over which sedimentary formations were in progress in order to make, finally, the Appalachian range, reached from New York to Alabama, and had a breadth of 100 to 200 miles, and the pile of horizontal beds along the middle was 40,000 feet in depth.  The pile for the Wahsatch Mountains was 60,000 feet thick, according to King.  The beds for the Appalachians were not laid down in a deep ocean, but in shallow waters, where a gradual subsidence was in progress; and they at last, when ready for the genesis, lay in a trough 40,000 feet deep, filling the trough to the brim.  It thus appears that epochs of mountain-making have occurred only after long intervals of quiet in the history of a continent."[1]

[1] Dana, Manual of Geology, third edition, p. 794

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On the western side of North America the work of mountain-building was, indeed, on the grandest scale.  For long ages and through a succession of geological epochs, sedimentation had proceeded so that the accumulations of Palaeozoic and Mesozoic times had collected in the geosyncline formed by their own ever increasing weight.  The site of the future Laramide range was in late Cretaceous times occupied by some 50,000 feet of sedimentary deposits; but the limit had apparently been attained, and at this time the Laramide range, as well as its southerly continuation into the United States, the Rockies, had their beginning.  Chamberlin and Salisbury[1] estimate that the height of the mountains developed in the Laramide range at this time was 20,000 feet, and that, owing to the further elevation which has since taken place, from 32,000 to 35,000 feet would be their present height if erosion had not reduced them.  Thus on either side of the American continent we have the same forces at work, throwing up mountain ridges where the sediments had formerly been shed into the ocean.

These great events are of a rhythmic character; the crust, as it were, pulsating under the combined influences of sedimentation and denudation.  The first involves downward movements under a gathering load, and ultimately a reversal of the movement to one of upheaval; the second factor, which throughout has been in