A central image in Mark Jenkin’s weathered, rough-hewn, rocky folk horror “Enys Men” is of a weathered, rough-hewn rock. A menhir that looks like it’s been orphaned from Stonehenge stands perched on a blustery hillside on the eponymous isle (pronounced Ennis Main, the Cornish for “Stone Island”). And just as many such ancient monoliths remain somewhat inexplicable, this striking cinematic anomaly appears as though excavated from the annals of filmmaking history, with the viewer playing the befuddled archaeologist faced with an uncanny artefact from a lost civilization. Shame that sometimes, such discoveries turn out to be more impressive for how they look than what they mean.

Shot by Jenkin himself, who also writes, edits and scores, the hand-processed, richly saturated “Enys Men” is warm to the eye and livid with gorgeous 16mm grain, glorying in a scratchy, imprecisely post-synced soundtrack. It follows — or trundles after, in ever-decreasing circles — a woman known only as The Volunteer (Mary Woodvine), who in the spring of 1973 is apparently the sole inhabitant of the island, if you don’t count all the apparitions.

She is involved in an obscure botanical research program that entails tramping from her pretty cottage across the island, past a ruin and a well, to measure the soil temperature at the same cliffside spot, then tramping back to record her findings. “No change,” she pencils in, day after day after day, before making a cup of tea, checking the gas levels on the sputtering generator, taking a bath and going to bed. Occasionally, a radio crackles. Sometimes she reads a book, though she never seems to get very far through it.

The woman’s solitary daily rituals are very much the point here, as they’re repeated with only the most minor of alterations: the size of the stone she throws down the well that day, say, or the angle of the shot of it leaving her hand. Still, by the fifth or sixth “no change” it’s hard to stop impatience setting in, especially as the attentive viewer will already have sussed that there’s something squirrely going on with the film’s internal calendar. A radio report refers to a memorial to the victims of a sea tragedy as having been erected in May 1973, though, as the Volunteer writes out painstakingly time and again, this is only late April. Eventually other glitches appear, like when she finds a cut flower and brings it home, only to be the one who cuts it a few days later. Or when she mounts on her mantel a piece of dripping flotsam salvaged from a boat wreck that either has not yet occurred, or occurred a couple of centuries prior. The rustic house she lives in seems overlaid with a memory of its own future dereliction. Blood drips from a wound she hasn’t yet sustained.

And there are more obviously eerie, supernatural trappings too, many of them slightly tired tropes given the recent resurgence of folk horror as a genre. There are visions of a creepy priest involved in some arcane ritual, as well as a chorus of young girls dressed in virgin-sacrifice white. And mimicking the sudden appearance of some mossy tendrils in the petals of the flowers she is studying, a line of lichen grows across the standing stone, in a similar pattern to the vaguely gangrenous, fibrous rash that starts to spread across the Volunteer’s belly. Eventually, the film takes on the character of a waking nightmare, though it must be said, not one that is ever actually very frightening.

The most remarkable thing about Jenkin’s excellent, BAFTA-winning 2019 breakout “Bait” was how much that film’s similarly experimental — though black-and-white — imagery complemented the story it told. A tale of gentrification, of traditional lifestyles and professions being pushed out by newer, less artisanal technologies, its aesthetic itself felt like an analogous celebration of old-school filmmaking in an age of digital sterility. Here, the defiantly creaky early-cinema techniques are extremely cool to look at (and listen to, given Jenkin’s brooding, evocative soundscapes), but feel thematically lost at sea.

There are, of course, references to bygone British cult classics like “The Wicker Man” and “The Blood on Satan’s Claw.” There’s a definite “Don’t Look Now” homage in the eye-popping bright red of the Volunteer’s raincoat. There’s even a little Kubrickian “You have always been the caretaker” vibe to some of the later twists, while Robert Eggers’ “The Lighthouse” provides a more recent touchpoint for the people-going-crazy-with-isolation-on-an-island subgenre.

None of these titles are remotely bad company to be in, but it’s hard not to be disappointed that where “Bait” referred so cleverly to issues outside the engulfing textures of its fascinating frame, here Jenkin only ever really refers to other movies. Visually and sonically, “Enys Men” is utterly intoxicating, but a lack of any nourishing interplay between form and content makes it feel like getting drunk on an empty stomach, alone on an island where everything happens at the same time, and nothing really happens at all.