unplumbed

Down, down, to what unplumbed depths had it gone, those other times?

Electricity for the ancients was an unplumbed ocean, whose slightest fluctuations affected them in ways they could not understand.

Did we really live on desert islands, cut off so wholly from each other by the unplumbed, salt, estranging sea?

Helen grew conscious of unplumbed depths, of instincts at which she was amazed and ashamed.