The Da Vinci Notebooks at sacred-texts.com
In this work you have first to prove that the shells at a thousand braccia of elevation were not carried there by the deluge, because they are seen to be all at one level, and many mountains are seen to be above that level; and to inquire whether the deluge was caused by rain or by the swelling of the sea; and then you must show how, neither by rain nor by swelling of the rivers, nor by the overflow of this sea, could the shells--being heavy objects--be floated up the mountains by the sea, nor have carried there by the rivers against the course of their waters.