Passage 8.15.1
Φενεάταις δὲ καὶ Δήμητρός ἐστιν ἱερὸν ἐπίκλησιν Ἐλευσινίας, καὶ ἄγουσι τῇ θεῷ τελετήν, τὰ Ἐλευσῖνι δρώμενα καὶ παρὰ σφίσι τὰ αὐτὰ φάσκοντες καθεστηκέναι· ἀφικέσθαι γὰρ αὐτοῖς Ναὸν κατὰ μάντευμα ἐκ Δελφῶν, τρίτον δὲ ἀπόγονον Εὐμόλπου τοῦτον εἶναι τὸν Ναόν. παρὰ δὲ τῆς Ἐλευσινίας τὸ ἱερὸν πεποίηται Πέτρωμα καλούμενον, λίθοι δύο ἡρμοσμένοι πρὸς ἀλλήλους μεγάλοι.
The Pheneatians have also a sanctuary of Demeter surnamed Eleusinian, and they celebrate mysteries in honor of the goddess, asserting that this rite established among them is the same as that performed at Eleusis. For according to an oracle from Delphi, Naos came to them, who they claim was the great-grandson of Eumolpus. Beside the sanctuary of Eleusinian Demeter stands a structure called Petroma ("the Rock"), which is formed by two large stones fitted together.