Mountains and valleys reshaping the terrestrial sphere
Over long ages peaks rise, valley floors sink toward the earth's centre, and mountain bases grow narrow
The sheet joins a drawn profile of mountains standing on the terrestrial globe to notes on how the earth's body changes over long ages: mountain summits keep rising, their opposite slopes draw together, and the floors of valleys sink toward the centre of the world. Leonardo adds that valleys deepen faster than mountains rise, that mountain bases grow ever narrower, and that the deeper a valley cuts, the more quickly its sides are worn away. A circle with a jagged upper edge, drawn at lower left, gives the profile of mountains on the sphere.
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Peaks rise while valley floors sink over time
Over long time the summits of the mountains always rise and their opposite sides draw nearer together, while the depths of the valleys, lying above the sphere of water, always approach the centre of the world. In equal time the valleys sink much more than the mountains rise, and the bases of the mountains grow ever narrower.
Deeper valleys wear their sides away faster
The deeper a valley becomes, the more its sides are consumed, and in a shorter time.
Profile of mountains on the terrestrial sphere
A drawn circle with a serrated upper edge shows the profile of mountains standing on the globe of the earth, illustrating the accompanying notes on erosion and the sinking of valleys.