How Rivers Carve Mountains from Land Risen from the Sea
Draining water furrows the emerged plain into valleys, peaks, and rock strata
Leonardo asks how, if the land of the antipodes upholding the Ocean rose and was uncovered almost flat, it would in time come to have mountains, valleys, and rocks in diverse strata; the muds and sands laid bare when river floods recede, he says, teach the answer. The accompanying passage traces the process: water draining off the raised plain begins as rivulets, digs itself deeper channels that gather the surrounding waters, and by consuming their banks leaves the ridges between rivers as sharp peaks. The drained hills then dry and harden into stone in strata larger or smaller according to the thickness of the muds the rivers carried. A small sketch at the right shows land furrowed by water courses, and further untranscribed writing stands in a box in the lower-right margin.
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Land of the antipodes rising: origin of mountains and strata
If the land that upholds the Ocean rose and was uncovered almost flat, how would it in time come to create mountains, valleys, and rocks of diverse strata? The mud or sand from which water drains when river floods recede teaches the answer.
Draining water carves the plain into rivers and peaks
Water draining off the raised plain starts as diverse rivulets in the lower parts, digging channels that gain width and depth as they gather surrounding waters, until the sides are so consumed that the ridges between the rivers become sharp mountains.
Drained hills dry and harden into layered rock
Once drained, the hills begin to dry and to create stones in strata larger or smaller, according to the thicknesses of the muds that the rivers had carried into that sea in their floods.