Gc and Gf
I think the Primeval Current and Wisdom of Stone were inspired by the concepts of fluid intelligence and crystallized intelligence, which are the two components in psychologist Raymond Cattell's theory of intelligence.
Raya Lucaria and the sorcerers have strong thematic connections to intelligence and mind, along with scholarship, reading, and other intellectual activities. More specifically, Raya Lucaria seems to have been inspired by Western scientists like Isaac Newton (credit to Quelaag), which makes it more likely that the Primeval Current is inspired by Western psychological frameworks. (Garrulous_Goldmask however has found connections between the Primeval Current and yoga; so there's a good example of Eastern influence.)
Cattell's model was later incorporated into a larger theoretical framework called Cattell-Horn-Carrol theory, which is probably the most widely accepted model of intelligence in the West. Fluid intelligence (Gf) is the ability or cluster of faculties that allows one to think through and solve new problems, and includes sub-faculties like working memory and processing speed. Crystallized intelligence (Gc) is equivalent to long-term memory, and therefore based on prior knowledge.
Under its common definition, wisdom would be considered a form of crystallized intelligence. Since crystallized intelligence is prior knowledge, there is a natural association with the "wisdom of the ages", of elders, ancients, etc. Thus, there is a psychological basis for associating wisdom with crystals and stone. Furthermore, since 'primeval' basically means "very old", the Primeval sorcerers likely possess ancient knowledge, which again, is commonly referred to as wisdom.
The Primeval Current is consistently associated with fear. This is most explicit in the description of Comet Azur, which reads: "When Azur glimpsed into the primeval current, he saw darkness. He was left both bewitched and fearful of the abyss." Azur's experience petrified him psychologically, but also physically; petrification is the process of turning to stone, i.e. crystal. Nonetheless, it should be noted that in Elden Ring, crystallization seems to turn the mind and body into a single substance, meaning there isn't a strong distinction between mental and physical processes in this context.
This is why I think Azur's and Lusat's bodies remain valuable to Sellen; though reduced to stone, the stone is imbued with their exceptional intelligence—which is perhaps more efficient at creating graven masses. Thus, if glimpsing the Primeval Current produces a body-mind synthesis, it makes sense that psychological petrification would occur simultaneously with physical petrification.
Upon reviewing Lusat and Azur's models, I noticed something that (I previously thought) could connect this idea of fear to the Wisdom of Stone, which is that both of them have their eyes covered. Originally—before I checked and realized that Azur and Lusat are wearing veils—I thought their eyes were covered by their crystal headpieces.
https://preview.redd.it/pwf9o7s21uza1.jpg?width=2560&format=pjpg&auto=webp&s=e08f5159e2d193a6b7a38cd1a08583b002caa1a6
The cloth blinds could be the Primeval sorcerer variant of the blinds worn Two Fingers prophets. Or perhaps Lusat and Azur were literally blinded by what they saw in the Current, and are wearing the cloth for the same reason as Irina/Hyetta. One could argue that in the context of the Primeval sorcerers, both of these are true. We know Wilhem the errant sorcerer has some connection to the Primeval Current, and he wears the Hierodas glintstone crown, which has the eyes covered by a red cloth. This could indicate his eyes were gouged out, similar to the thorn sorcerers. (Perhaps the Primeval sorcerers removed their eyes in an attempt to avert their gaze?) Yet, the crown was bestowed to sorcerers before departing the academy, which means the blindness symbolism is not entirely due to physical blindness.
It's also possible the blinds were used to enhance one's vision into the Primeval Current. Since the current is dark and abyssal, then perhaps by constantly looking into their blinds, the sorcerers' eyes would adjust to the darkness, allowing them to see more stars in the Current. After all, adjusting one's eyes to the night sky is an inevitable part of stargazing.
As mentioned, I originally thought it was the crystal itself that was covering their eyes. The interpretation I developed was that both characters are hiding in the Wisdom of Stone, using crystallized, wisdom-imbued helmets—or that they might be blocking their vision to cease their observation of the Current, or attempting to "hide" from the Current by taking advantage of object impermanence; in other words, they might be trying to make the Primeval Current "go away" by covering their eyes. Since the effects of observing the Current only occur through observation, this seemingly childlike technique is probably effective; The Primeval Current is object-impermanent.
To hide in stone might seem counterintuitive if stone represents fear; but stone is also protective, as demonstrated by the ancient dragons, and perhaps (more symbolically) by turtles hiding in their shells. This thematic pairing is repeated in the coffin cutscenes played when traversing the waterfalls: paradoxically, the coffin—a symbol of stone, death and fear—is entered in order to avoid death. Another closely related theory I shared in my previous post is that Lusat might be hiding from the Primeval Current in the Sellia Hideaway's purple (associated with gravity and fear) glintstone. If this is true, it would make the general "hiding in stone" theory more likely.
Wisdom is something that protects against, and is very often contrasted with, the fear that tends to accompany experience of the unknown. When faced with a frightful and novel situation, we might recall short sayings and saws, perhaps repetitiously. Religious people are likely to meditate on verses from their scriptures. Recall of these sayings and verses is technically a form of crystallized intelligence, unsheathed from memory (like a crystal sword) to help us in these encounters. Thus, the Wisdom of Stone helps defend against unpredictability and chaos—and I believe Azur and Lusat might be using this wisdom to shield their perception of the Primeval Current. Crystals, I'd like to note, have a highly ordered state of matter; a "crystal structure" is sometimes loosely defined as the ordering of any solid material, which would make crystals a suitable weapon against chaos.
Imagination
Although the concept of crystallized intelligence seems to have been left mostly untouched in Elden Ring (besides its being literalized as physical crystals), I believe the concept of fluid intelligence was replaced with imagination. Part of what led me to this theory is the connection between the Primeval Current and intelligence/psychology. If perception is tied so heavily to the Primeval Current (fear, vision, etc.) one could reasonably speculate the Primeval Current has something to do with consciousness.
However, the primary evidence for this theory is the description of the Founding Rain of Stars:
"The glimpse of the primeval current that the astrologer saw became real, and the stars' amber rained down on this land."
If the glimpse of the Primeval Current is something that became real, this would suggest it was something unreal to begin with.
I've also been thinking that the influence of Lovecraft on the Primeval Current could be a hint that it's rooted in the imagination. This is because what breaks the minds of Lovecraft's characters is the inability to comprehend, i.e. to imagine, the deities described. A similar kind of brain-blasting horror exists in Hellraiser, which was an influence on Elden Ring as well as Berserk.
More speculative evidence is the onyx and alabaster lords. Others have likened them to dark elves and light elves, which have become classic creatures in high fantasy. As such, it would be fitting if such creatures are fantastical, even within the world of Elden Ring; in other words, if they originate from the mind. Something else that comes to mind is Terence McKenna's "machine elves" anecdote, which further links elves with psychospiritual experiences, and with fantasy.
There's of course the line from Sellen about "opening our minds", which would make more sense if it's referring to imaginative capacity than fluid intelligence. Consciousness is arguably closer conceptually to imagination than fluid intelligence, although the latter does nonetheless affect our perceptions of things (e.g. through working memory), and thus our consciousness.
The last thought I had for this section has to do with Sellen's view of the stars as living things, which she shares at the beginning of her quest and repeats at its end. To summarize: the Primeval sorcerers view the stars as living things, while the majority of glintstone sorcerers do not. What does this imply about the Primeval sorcerers and Current?
For one, it reveals the Primeval sorcerers have a more ancient way of thinking than modern sorcerers. Stars, for a significant length of history, were indeed interpreted as living things: as gods and mythological figures. This could be one reason the sorcerers and Current are called "Primeval"; they represent an older and more mythological way of looking at the night sky. Once again, there is an association here with fantasy and imagination. Though it might not be true in a technical sense, we often think of ancient peoples as having possessed greater imaginations than us (even though this was often the consequence of limited knowledge).
More thoughts on psychology, and why Sellen might have succeeded
In addition to imagination, the Primeval Current might be equivalent to collective consciousness.
The user M00n_Slippers had the theory that the waterfalls in the underground could be representations of the Primeval Current, and I think this is correct. More recently, I watched a video by TheCenteredTarnished ("Elden Ring Lore: The Great Works Part 1") who points out that in depth psychology, collective consciousness or unconsciousness is sometimes compared to a waterfall.
For background, the Primeval Current is already linked conceptually to souls, since there is linguistic similarity between "Primeval Current" and "primal glintstones", which are used by the Primeval sorcerers. And souls are equivalent to consciousness, hence the word 'psyche'. So if the Primeval Current is represented with waterfalls, and waterfalls are representations of collective consciousness—and the Primeval Current is already equivalent to consciousness—then the Primeval Current might be collective consciousness. After all, the Primeval Current is parallel (if not equivalent to) the Primordial Crucible, which is a union of all life melted together into a collective. This movement toward collective unity should also be present in the Primeval Current then; evidence for which is the graven masses, which are clusters of sorcerers grafted together.
Sellen's graven mass
Since the graven masses are collections of heads (and minds), and these heads seem to be severed from the rest of the body, I think the idea is that they are simultaneously the result of knowing too much, and of consequently "losing their heads", thus ultimately knowing nothing. It's a clever way of expressing the dangers of excess curiosity, which have often been described in this paradoxical fashion.
Related to this is the fact that Sellen's glintstone crown is cracked. This could be an omen of her death, since Destined Death is often symbolized as a black gash. The crack also reminds me of the evergaol rifts, which I believe are associated with the Primeval Current, and probably Destined Death. As it pertains to psychology though, or at least idioms about it, I think the joke is that Sellen "opened her mind so much her brain fell out."
Despite the symbolism of the graven mass, it's been speculated that Sellen's experiment may have been a success. There is actually some support for this interpretation which I'd like to share here.
In multiple item descriptions, the Crystalians are said to possess a "faint cogitation". The descriptions equate this faint cogitation with the Wisdom of Stone. Now, it seems clear enough that Sellen's consciousness is also faint. While she might be in too much pain to speak, it's also possible her mind has been mostly destroyed. Thus, since Sellen becomes stone, and has a faint cogitation after turning into the graven mass, this could be evidence she achieved what she sought. By the way, I think this is also seen in Azur and Lusat: they also seem to possess a reduced form of consciousness. They don't even seem fully aware of their surroundings or their interactions with us.
Both the Crystalians and Primeval Sorcerers (or Azur at least) are found in meditative poses. "Faint cogitation" could be an allusion to Eastern practices of meditation, many of which involve a slowing and calming of the mind's thoughts. So even though experiencing the Primeval Current might be like an overload of consciousness, perhaps the desired result is consciousness that's been reduced? I think this calming of the mind could be represented physically as petrification and solidification, which I'll discuss in the two sections below.
The Nature of the Primeval Current
1.) Gravity
I've talked about the connection between gravity and the Primeval Current before, so here I'll add something I haven't shared yet: 'Graven' and 'gravity' start with the same letters. And mass is the source of gravitational attraction.
In my previous post, I raised the idea that Lusat could be using the Sellia Hideaway to hide from the Primeval Current. Some opposing evidence for this is that the Sellia Hideaway is filled with purple glintstone, i.e. gravity glinstone. In Elden Ring, gravity, stone, and purple are all associated with fear—so it could be said that Lusat is hiding in a symbol of fear. Could this contradiction exist for the same reason Azur and Lusat "hide" in crystals, or for the same reason stone coffins (fear and death) are used to avoid death?
The user Kotoy77 recently submitted a post showing that Azur is levitating. This means both Azur and Lusat have associations with gravity, and that this could be true for the Primeval Current as well.
Sidenote: Azur's and Lusat's robes have crow/raven feathers, which explains Azur being on Mt. Gelmir and provides a connection to the assassins of Ravenmount, who wear the Raptor's Black Feathers. This also strengthens the link between the Current and Gloam-Eyed Queen, who has many associations with Gelmir.
2) Outer space
Last Protagonist has shown that Japanese descriptions of Astel more explicitly associate him with darkness, which is what the Primeval Current is said to contain per the description of Comet Azur. Since space is darkness, and both Astel and the Primeval Current are thematically linked to fear, this seems to narrow the conceptual gap between the Primeval Current and outer space in general, and could mean they're same thing. I don't think I'm the first to suggest this; to my recollection it was M00n_Slippers.
3) Aether
The above theory makes more sense when we consider that outer space was once thought to contain a medium called aether, which was believed to be a liquid. The aether theory, like the belief that the stars were deities, is an older and thus comparatively primeval understanding of the cosmos.
4) Vacuum space
Suppose that outer space in Elden Ring does not contain aether or current, and that it's nothing but darkness and void. Purely empty space is called a vacuum. Vacuums suck things in, which would hypothetically create a current. So the Primeval Current could be the movement created from empty space itself. Alternatively, since vacuum space has no color, i.e. is black, maybe the current instead produces black holes—which would bring us back to the gravity interpretation.
5) Tides
I've also theorized that the Primeval Current could be the ocean's tides, in a post about how Elden Ring's moon has imprinted on it a part of the gravity sigil. In a comment on this post, slapmyasswithtuna pointed out what this meant: the gravity sigil is on the moon because the moon exerts a significant gravitational effect on Earth, and vice-versa. From this I proposed that the Primeval Current could be the tides, as well as Destined Death, as the oceans both give birth to life and return it to the ocean.
6) Liquid crystals
In an older post of mine, I played with the idea of the Flask of Wondrous Physick containing a liquid crystal substance, like in a liquid crystal display (or LCD), since it's a flask you drink from (liquid) that contains crystallized tears. The comparison to LCDs is more appropriate in the context of the Primeval Current, since the only sense used to observe the Primeval Current is sight. So it makes a surprising amount of sense that the Primeval Current, a liquid, is displayed to sorcerers who are made of crystal. (Also, this is a dumb thought but LCD is one letter away from LSD, which I think is more or less what looking at the Primeval Current is like.)
In summary, I think the Primeval Current could be any or all of the following: imagination, collective consciousness, gravity, outer space, vacuum space, aether, tides, and a liquid-crystal substance.
More on nature
In Elden Ring, liquids can potentially turn to stone if they're left stagnant. My evidence for this is the stone columns in the Lake of Rot, which are very likely petrified trees, since their cross sections on the map look the same as Godwyn's tree and the Erdtree in Deeproot Depths. I believe this indicates that rot, i.e. stagnation, turns things to stone by killing them, resulting in petrification. Thus, it seems that the slowing of current produces stone, which I believe is also occurring psychologically as the Primeval sorcerers meditate. That stagnation can turn liquid to stone could be expressing how different energies and particle motions are required for liquid and solid states.
The reverse is more intuitively true, and true to life: increasing the "flow" of stone, i.e. by heating it up, would energize the particles and melt the stone, resulting in a current. To me this sounds very similar to the function of the Crucible.
Something else I find interesting about the Wisdom of Stone is that it simultaneously seems to obey and fight against the Primeval Current. Of course the two are connected, and might even be the same because that's a huge theme in Elden Ring. But still, a solid is nonetheless considered an opposite of liquid. This inconsistent relationship might be expressed through the Primeval sorcerers seeking wisdom in the Current, but also hiding from it in the Wisdom of Stone.
This relationship can be visualized a little more clearly if we imagine the Wisdom of Stone singularly as stone (easy enough), and the Primeval Current variably as water and gravity. (I like this framework because the Wisdom of Stone is appropriately interpreted as a static concept, while the Primeval Current is interpreted dynamically, like liquid.)
Stone obeys gravity because it falls, is heavy, etc. But in an environment like a river, stones resist current and force it to move around it. The former example would represent the Primeval Current and Wisdom of Stone as a unified entity, while the latter would express their opposition.
As such, it could be said that the movement of the stone coffins from the edge of the falls to over them represents the switch from resisting the Primeval Current to submitting to it. (Credit again to M00n_Slippers.) I think this transition could also tie into the Primeval sorcerers "seeing beyond" the Wisdom of Stone. If the Wisdom of Stone is also something that must be surpassed, in addition to sought, maybe the interpretation that must be overcome is the idea of stone resisting flow—in exchange for the view that stone must submit to it.
Note: I did check the waterfalls in the underground, and unfortunately for this theory, the water is flowing under the coffins unobstructed.
Or, if miirshroom's theory is right and overcoming the Wisdom of Stone involves overcoming gravity, perhaps the aim of this intellectual journey is to understand that gravity and currents can be reversed, and are bidirectional. This could be evidenced by the cutscenes where we ascend the waterfall in the stone coffin. The pull of the current in both directions could be compared to the alabaster and onyx lord's pull/repulsion, which likewise map onto regression and causality. Since both are required to "be complete", maybe the key to enlightenment is understanding that forces which submit to and oppose the Primeval Current are equally important, and must both be integrated.
Religious and cultural inspirations
The duality of the Primeval Current and Wisdom of Stone might have been inspired by the Biblical account of Moses striking the rock with his staff, and releasing the water inside. The game already has the ancient dynast, who looks a good deal like the common image of Moses holding the Ten Commandments.
The typological parallel between this story and the water that poured from Jesus's body when he was speared may have been made more explicit through the fact that Marika, who is also crucified and speared, is made of stone. Thus, since Marika is a vessel of the Elden Ring, i.e. a crucible, she might contain the Primeval Current within her: the Elden Beast, which is filled with stars. The possibility of the Elden Beast being the Primeval Current was suggested by Gideon the Half-Knowing, who pointed out the significance of Sellen's request to us, that we "lay bare the secrets of life which course the Elden Ring", i.e. the Elden Beast. (In case this wasn't noticed: a current is something that "courses".)
I'd be remiss if I didn't try connecting the "draining of liquid from stone" concept with the visual of cracked crucibles spilling their contents, which I recently discovered is a very important symbol in the game. So I think that the Primeval Current emerging from cracks in the Wisdom of Stone (if that part is right) is equivalent to the leaking of fluid from stone crucibles.
Another reference material for the Primeval Current may have been Stanley Kubrick's 2001: A Space Odyssey. This is something I'd considered early on, but there's more evidence for it than I thought. On its face, the Primeval Current has a good deal in common with the torrent of stars in the Stargate sequence, which is part of the third act of the movie, called "Jupiter, and Beyond the Infinite". Both are experienced as an overload of consciousness: otherworldly, overwhelming, and terrifying. And the variously colored stars and celestial phenomena in the Stargate sequence potentially tie into Elden Ring's emphasis on color.
crystals from 2001: A Space Odyssey
In addition to stars, the Stargate contains blue octahedral shapes; these influenced Laputa's crystalline energy source in Hayao Miyazaki's Castle in the Sky. In Elden Ring there's an association between 8-pointed shapes and stars, and similar to 2001, there's a juxtaposition of current (colors, stars, etc.) with blue crystals, in particular. The coupling of red and blue in the segment shown above might be significant, as this is probably the most fundamental color pairing in Elden Ring. You can even see a bit of purple in the shot above!
There's more evidence that Elden Ring is taking notes from 2001. Others have compared the game's memory stones to the film's black monoliths. In the movie, the Stargate sequence is initiated by the monolith rotating on its side (so the audience is only looking at its depth), causing it to blend in with the blackness of space. Almost immediately after is the emergence of light and color from the void, which suggests the stars could be emerging because of (or from) the monolith, which is what triggers evolution and higher consciousness in the movie. Here again, we have a liquid emerging from stone. (The root 'lith' in 'monolith' means "stone.")
There is yet another possible media inspiration behind the Primeval Current. Azur's and Lusat's skulls turned to crystal—which could be a reference to Indiana Jones and the Legend of the Crystal Skull, which, like 2001 and Hellraiser, is about forbidden knowledge/experience that destroys people.
To conclude: Given what I wrote in the earlier section about current turning to stone, and in this section about stone releasing water, it could be said that stone is what contains the Primeval Current, as well as what it turns into.
Differences with Raya Lucaria
After understanding more clearly that the Primeval sorcerers view stars as sentient, and that many glintstone sorcerers do not, I started to notice the bifurcation of sorceries which could be loosely described as stellar (Primeval) and the remaining glintstone sorceries. For example, every spell that mentions stars or celestial objects is part of either the Olivinus or Karolos conspectuses, i.e. Lusat's or Azur's. The one exception is the spell Starlight, but this is said to be "Granted to sorcerers who depart from the academy to embark on journeys." I interpret this as saying it was given to exiled sorcerers, similar to how the Hierodas glintstone crown may have been given to outcast scholars, or how the red hood was granted to Roderika as part of her banishment. Thus, I believe this sorcery is closer to the Primeval conspectuses than it originally seems.
Sidenote: the remainder of the description for Starlight reads: "Even during the blackest nights, sojourns underground, or imprisonment in gaol, the stars are never far from a sorcerer's side." I believe the second part is pretty clearly alluding to Lusat, and the first part is probably referencing the Nox, if it's not also about Lusat. I'm not sure if it's saying Lusat was using the stars as guidance/comfort, or if this is "dark" humor, since I've theorized Lusat might be running from the stars instead. (To be clear, what Lusat observed in the Primeval Current was not the abyssal darkness Azur saw, but a shattering star cluster.)
In opposition to the Primeval sorcerers, the glintstone sorcerers use spells and abilities that emphasize the concreteness, physicality and terrestrial nature of their worldview. One example is the Cannon of Haima spell, which is a mortar attack. Mortar is both the material used to bind stones together, as well as a bowl, like a crucible (e.g. in a mortar and pestle). Another important example is the glintstone drills used by the miners, and the act of mining glintstone itself.
Sellia Crystal Tunnel
I think the glintstone mining might represent, among other things, the pillaging of the earth. The Elden Beast, as many have noticed, looks a great deal like the Forest God from Princess Mononoke. And as mentioned, in Sellen's penultimate dialogue she hints she might know something about the Elden Beast. Sellen of course has a worldview that integrates the stars; now, in addition, she is associated with the Elden Beast, which resembles the Forest God. The glintstone sorcerers are the inversion of this, and are closer instead to Lady Uboshi and Irontown. They mine for natural resources, at the price of damaging the earth. The product is glintstone sorcery, i.e. a technological transformation of a natural material, like the use of iron in firearms. (By the way, Sekiro, which was developed simultaneously with Elden Ring, has its own version of Irontown: the Gun Fort.)
An interesting case to consider is the sorcerers' head-butt attack. I think this attack could parallel their book-smack move, because books, like stone, contain wisdom (e.g. the stone on the glintstone crowns) and would thus serve as appropriate weapons.
The books might be symbolic of something else, too: the transition from looking up at the sky, as an astrologer would, to looking down, toward the earth, and learning from what is recorded, and "set in stone". In this sense, they are quite similar to the miners, who they likewise look down upon. I believe Sellen's criticisms of the bookworm scholars is showing the contrast between learning from direct experience, and learning from study. Remember as well that Sellen detests the "pedantry" of the academy. Pedantry is placing too much attention on semantics: in this context, runes, language, etc.
Scholars reading in Raya Lucaria
"Toothless pedantry" is a brilliant insult. First, it implies the Primeval Current is toothed, like the Crucible, and thus may be associated with it in some way. Moreover, it suggests the Academy is talking (pedantry) without teeth, which would make their ideas difficult to understand—since teeth, in addition to biting, chewing, etc., also help us annunciate. It's another criticism of corrupted intellectualism that references another common saying about intellectuals: that they "talk much while saying little".
Probably the best example of the distinction between the Primeval and glintstone sorcerers, within Raya Lucaria, is the Church of the Cuckoo. For this topic I'd like to reference and thank Lutana who came up with an amazing theory on the significance of the cuckoo and let me reference their idea. They suggested it might be a symbol of insanity, and that Raya Lucaria might be something like a mental institution, referencing Bloodborne's upper Cathedral Ward and One Flew Over the Cuckoo's Nest.
On its face this might not make sense, because we know Raya Lucaria banished the Primeval sorcerers for their association with the Primeval Current. But this interpretation actually helps to explain many things about the Church of the Cuckoo. It explains why the only graven mass in Raya Lucaria is found in a room connected to and only accessible through the Church. Above this graven mass is the only place that artificial stars can be found in the academy. It explains why there's a Crystalian sorcery on the upper level, why the Twinsage conspectus crown is found right outside the Church, and why the only two Olivinus conspectus sorcerers in Raya Lucaria are inside the church. The Olivinus conspectus was dedicated to the study of meteors, which are the same as stars, because meteors are shooting stars.
Here is an Olivinus conspectus sorcerer in the Church of the Cuckoo. Note: I later found Olivinus conspectus crowns on the wall of glintstone crowns before the Red Wolf of Radagon fight, but these are just masks and aren't worn by the sorcerers here.
To my understanding, this means these two sorcerers are the only ones in Raya Lucaria to use star sorceries; though the twinsage sorcerers seem to use crystal spells, which are Primeval. This isn't too surprising though, since we know the Twinsage sorcerers were granted the privilege of using sorceries of all kinds.
The Church of the Cuckoo being dedicated to the Primeval Current might also have something to do with the Inverted Carian Statue on the altar, since the Carians' moon-focused ideology was viewed as opposing the Primeval Current, with its emphasis on stars. My guess is that the church was an original part of the academy, since the academy used to permit investigation into the Primeval Current. The church wouldn't have been used for this purpose during Rennala's leadership, but it may have regressed to its original function once Rennala was overthrown. Maybe this is what the inverted statue represents.
Something I find intriguing about Rennala's ascension in the academy is that it suggests the sorcerers of the old academy were partially justified in their fear of the moon being made equal to the stars. The theorist St. Trina postulated this could represent the fear of feminism and equal rights, with stars being masculine and the moon feminine. Feminism and other movements centered around social equality have often been denigrated as attempts to make the disadvantaged group in question superior to the advantaged group.
This seems to be what the stellar sorcerers were afraid of—but ironically I think this actually happened in the case of Raya Lucaria. Rennala's full moon was said to "bewitch" the academy; but Rennala is in fact a witch, since she is a magic-wielding woman. Moreover, as stated earlier... there is only one place in Raya Lucaria that contains stars, and that's in the Church of the Cuckoo. On the other hand, astronomical devices containing the moon are found in multiple places in the academy (you can see one on the Raya Lucaria loading screen).
Here's a thought: if stars are interpreted as masculine, then the Church of the Cuckoo might also in some sense be loyal to Radagon. The sun is a star, and Radagon is associated with the sun, particularly in Liurnia where the Erdtree and moon form an eclipse. People have also speculated that Radagon might be the cuckoo, since he leaves Rennala the golden egg. (This interpretation seems to have obscured the insanity theory; in retrospect, Iji's pronunciation of the word cuckoo as "coo-coo" makes the association a bit clearer.)
So I think that even if the Church of the Cuckoo was not originally built to worship Radagon, it may have become compatible with this purpose as a place for worship of the masculine spirit, which might have been desirable to those dissatisfied with Rennala's moon-themed (feminine) leadership. Yet, both objects of worship can eventually result in insanity: star worship leads to graven masses and lost heads, while moon worship leads to lunacy. (Rennala's "diagnosis", other than lunacy, is probably hysteria, since as Miss Chalice pointed out, she caresses the amber egg like it's her pregnant abdomen. And the word 'hysteria' is etymologically linked to the uterus.)
Post is continued in the comments below.
Radagon's statue placement kind of makes it look like he's pulling her strings.
Update: I'd like to propose a more physical explanation for the description on the Primeval Current "becoming real". This idea came to mind after I left a comment on the visibility of the Erdtree, explaining that when viewed through the telescope, the Erdtree will only ever appear as solid. The user "flowbro (kirby)" suggested this could be a representation of the wave function collapse, since the Erdtree only becomes "real" when it's observed. The quantum mechanical theory in question is the Copenhagen interpretation. I believe the same principle could apply to the Primeval Current, and that the Current is quantum potential that only becomes determinate when interacted with: in this case, when observed visually. More evidence is that quantum potential is sometimes called "quantum foam". Both foam and currents are liquid, and part of water systems. Foam in particular ties into the tidal theory of the Primeval Current, described above.
Update 2: I missed something on the relation between the Primeval Current and Raya Lucaria.
The Primeval sorcerers are astrologers, and seek to make the culture of sorcery more like it used to be, when it was integrated with astrology. Since Elden Ring is a medieval fantasy, I had just assumed that astrology was the closest thing in the Lands Between to astronomy. But I think I was overlooking how astrology is the more ancient, primeval basis for astronomy. The Primeval Sorcerers may seek a revival of astrology because it is older and more magical than the current magical culture, which is analogous to astronomy: resolutely unmagical.

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