Passage 8.42.1
τὸ δὲ ἕτερον τῶν ὀρῶν τὸ Ἐλάιον ἀπωτέρω μὲν Φιγαλίας ὅσον τε σταδίοις τριάκοντά ἐστι, Δήμητρος δὲ ἄντρον αὐτόθι ἱερὸν ἐπίκλησιν Μελαίνης. ὅσα μὲν δὴ οἱ ἐν Θελπούσῃ λέγουσιν ἐς μῖξιν τὴν Ποσειδῶνός τε καὶ Δήμητρος, κατὰ ταὐτά σφισιν οἱ Φιγαλεῖς νομίζουσι, τεχθῆναι δὲ ὑπὸ τῆς Δήμητρος οἱ Φιγαλεῖς φασιν οὐχ ἵππον ἀλλὰ τὴν Δέσποιναν ἐπονομαζομένην ὑπὸ Ἀρκάδων·
The other mountain, Elaion, is about thirty stades distant from Phigalia; there is a cave there, sacred to Demeter surnamed Melaine ("the Black"). The Thelpousians' account concerning the union of Poseidon and Demeter is the same as that held by the Phigalians; however, the Phigalians assert that the offspring born to Demeter was not a horse but the goddess whom the Arcadians call Despoina ("the Mistress").