Thanks for your inputs all!
@freakofnature couldn't be, because he quotes that passage a few pages later ("地震を引き起こす 地中の空気 によって陸地が 冠水するように なつているのか...またそれが引く時は 大地の内部に 弓き込まれて いるのか" If you want to see what Latin looks like in Japanese)...
I found "while the sea is stirred up from the very bottom, and the monsters are driven from their depths and rolled upwards on the crest of the billow" (HN 9) so went with that as offering the most Plinian language—so I agree with
@sylvacoer that it's a (slightly anachronistic) pastiche.