The “strange tale of the future” Margaret Brundage was illustrating for this May 1938 issue of Weird Tales appears to be Seabury Quinn’s “Goetterdaemmerung.” (In 1938 umlauts were scarce, apparently.) Virgil Finlay did a lot of interior work on this issue, including this illustration for the title story:

Finaly also illustrated what looks to my eyes like a bit of the old ultraviolence about to happen for Edmond Hamilton’s “The Isle of the Sleeper.”

This issue of Weird Tales is available to read and download at the Internet Archive.