From Google:
"Although etymology indicates that Zeus was originally a sky god, many Greek cities honored Zeuses who lived underground. Athenians and Sicilians honored Zeus Meilichios ("kindly" or "honeyed") while other cities had Zeus Chthonios ("earthy"), Katachthonios ("under-the-earth) and Plousios ("wealth-bringing"). These deities might be represented indifferently as snakes or men in visual art. They also received offerings of black animal victims sacrificed into sunken pits, as did chthonic deities like Persephone and Demeter, and also the heroes at their tombs. Olympian gods, by contrast, usually received white victims sacrificed upon raised altars."
$10