The logical conclusion for Darwin was that a portion of the molten rapidly spinning Earth must have separated from the main mass and spawn off to become our Moon.
Certain points, crises, certain feelings, joys, griefs, and amazements, when reviewed, must strike us as things wildered and whirling, dim as a wheel fast spun.
The magnetic field of that material (and from the black hole) coil around, wound up by the rapidly spinning disk, pointing up and down out of the disk and away from the black hole.