XIII.xxii.ii. Primum diluvium extitit sub Noe, quando hominum sceleribus offensus Omnipotens, toto orbe contecto, deletis cunctis, unum spatium caeli fuit ac pelagi. Cuius indicium hactenus videmus in lapidibus quos in remotis montibus conchis et ostreis concretos, saepe etiam cavatos aquis visere solemus.
13.22.2. The first flood occurred during the time of Noah, when the Almighty was offended by the sins of men, the entire earth was covered, all was destroyed, and sea and sky were a single expanse. Down to the present, we see evidence of this in the stones we have become accustomed to seeing on remote mountains, stones that have solidified around shells and oysters, and also often stones that have been hollowed out by the waters.
[Update: I've posted extended excerpts from Isidore of Seville in my Library.]