The Da Vinci Notebooks at sacred-texts.com
The relative height of the surface of the sea to that of the land (942-945).b d is a plain through which a river flows to the sea; this plain ends at the sea, and since in fact the dry land that is uncovered is not perfectly level--for, if it were, the river would have no motion--as the river does move, this place is a slope rather than a plain; hence this plain d b so ends where the sphere of water begins that if it were extended in a continuous line to b a it would go down beneath the sea, whence it follows that the sea a c b looks higher than the dry land.
Obviously no portions of dry land left uncovered by water can ever be lower than the surface of the watery sphere.