As a child, we had a book of scary stories that included some absolutely ghastly but entrancing pen-and-ink art. I'm 99% sure they're not "Scary Stories to Tell in the Dark". I don't remember much, but a few things stuck with me:

• a picture of a diver in an old-timey deep sea diving suit and maybe a sea-witch type character draped in seaweed.
• at least one really creepy drawing of a willow tree
• one or more of the pictures also involved a classically gothic cliffside along the sea.
• I want to say the binding was green or teal
• no dust jacket that I recall, but it could have been missing
• as a child, it struck me as old but not ancient, so I'm guessing it was from the late 60s or early 70s maybe
• my parents let me read it, and they were Mormons and frankly not really readers, so I'm guessing it was sort of vaguely considered age appropriate in those days if parents didn't look too close.

Style-wise, as I recall it kind of split the difference between Edward Gorey (thanks, @flyingsquid@lemmy.world for unearthing my nightmare fuel) and the semi-famous Darth Maul concept art from Iain McCaig. I have downloaded the first two volumes of SStTitD, as they are technically old enough to be the ones, but while they're definitely in the same milieu they're not what I'm thinking of. The art in this had heavier linework and IIRC used pen-and-ink crosshatching instead of shading; I also can't find any images in those two that hit me as "THAT'S IT!".

This could absolutely be a wild goose chase down memory lane, but any suggestions?