bas-relief and antediluvian

ヘレン・ケラーの "The Story of My Life" に化石の話が出てきますが、まるで化石が見える様な文です。
Once a gentleman, whose name I have forgotten, sent me a collection of fossils--tiny mollusk shells beautifully marked, and bits of sandstone with the print of birds' claws, and a lovely fern in bas-relief. These were the keys which unlocked the treasures of the antediluvian world for me.
"bas-relief" と "antediluvian" は知らない言葉なので辞書を見ます。　まず、 "bas-relief"を調べます。
・Merriam-Webster's Online Dictionary: sculptural relief in which the projection from the surrounding surface is slight and no part of the modeled form is undercut; also : sculpture executed in bas-relief
・Century Dictionary: Low relief; in sculpture, a form of relief in which the figures or other objects represented project very slightly from the ground. The most artistic examples of bas-relief often present to the observer the illusion that their carving has considerable projection. A bas-relief, or a work in bas-relief, is a piece of sculpture in this form. Compare alto-rilievo and mezzo-rilievo.
"alto-rilievo" を見ると、"High relief; sculptured work in which the figures project more than half their thickness." とありましたので、"mezzo-rilievo" はその中間である事は調べずとも分かります。 "bas/mezzo/alto" は音楽用語で聞いた事がありますね。
さて、"antediluvian" は "diluvian" の前の時代を意味するようですが、いつの時代でしょうか？
・Compact Oxford English Dictionary:
　1. of or belonging to the time before the biblical Flood; gigantic bones of antediluvian animals
2. chiefly humorous, ridiculously old-fashioned: they maintain antediluvian sex-role stereotypes
なるほど、元々の意味はノアの洪水前の意味だったのですね。