This verse reads as a whole,

They break a shaft away from man's abode;

They are forgotten of the foot;

Far away from men they hang, and swing.

The first clause, lit. away from the dwelleror inhabitant, describes how the miners sink their shaft deep down below and away from the abode of men above. There they are forgotten by the foot of those overhead, who walk oblivious of them. And the last clause describes how they "hang and swing," i.e. swing suspended in cages or from ropes as they pursue their unnatural operations

half way down

Hangs one that gathers samphire dreadful trade.

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