Definition of "unlifting"

Do you know what pain treads the unlifting darkness with cleft hooves, with webbed feet?

1979, Poetry Australia, numbers 70-72, page 67

For Faulkner, these years marry professional triumphs and personal disappointments: the Nobel Prize for Literature and an increasingly unlifting depression. For Joan, these years were a tempest of youth and a burgeoning literary career.

2006, Lisa C. Hickman, William Faulkner and Joan Williams: The Romance of Two Writers

There had been no collieries on this side of the line, and now that the murky atmosphere, which had been an unlifting blight upon the midland plain, was gone for ever, the fields showed as fairly as though no pollution had ever touched them.

2010, Sydney Fowler Wright, Deluge, page 94