MEDDLING WITH FORCES

An idea has emerged for a compendium project next year. I need a series of short stories in the public domain that deal with people who "meddle with forces they cannot possibly comprehend" and summon dark and ancient magics.

The quote itself is from Indiana Jones, but the idea is much older. I so far have the following material:

1 - O Whistle and I'll Come to You My Lad (M R James)
2 - One of the 'John Silence' stories by  Algernon Blackwood
3 - Something by Robert Chambers (most of his stories about about meddling)
4 - The Merewigs by Sabine Baring-Gould

I'm hoping to get recommendations for this enterprise.