A/N: I shortened this chapter a little and changed some dialogs, especially at the end. So it's not that tedious anymore x)
...

„It must be somewhere down here, I'm certain of it!", said Ford with lowered voice and kept his eyes on scouting around.

Right behind him and hot on his heels there was Dipper, doing the same while their stony way was only illuminated by the dull shine of an old lantern and hardly prevented both from almost stumbling over stones here and there.

Just a few hours ago Stanford was sitting in the Shack, browsing through the journals in hopes that something useful got overlooked, undissolved on the first sight but maybe decoded on the second. Because the time was running, the rift was slowly cracking and a solution was badly needed. Not imaginable what could happen if Bill gets his greedy hands on the orb or finds another way which they didn't consider yet.

And so he decided to look for the deep caves of Gravity Falls where he once found the ancient petroglyphs of the dream demon and his cipher wheel. Maybe he could find something he accidentally missed back then, hidden parts he did not register.
And Dipper, of course, wouldn't even think of missing that chance when Ford asked to go with him.

"Uh, Grunkle Ford?" Dipper looked around in unease as the dark shadows seemed to follow them on the cold rock walls. "Are you sure that we didn't get lost? We've been going deeper for at least an hour now…"

"Of course I am, trust me. Those tunnels are indeed extensive but not as branched as they might seem, Dipper."

And as he had finished his sentence the man could see the reason for their dungeon trip, slowly revealed by the shine of his lamp.

"There it is, look!", he pointed out eagerly and stepped closer to the stony wall where the old cave paintings were still clearly visible, "Just as I left them..."

"Woah...", the kid behind him raised his head and followed, "This is where you got the clues and symbols of Bill? How old can they possibly be?" Dipper took a close look at the well-known drawing of the wheel, the 'one eyed demon' right in the center.
On the one hand it amazed him to stand right in front of a real and nearly untouched ancient writing, but on the other hand it gave him the creeps by the idea how old and powerful Bill could really be, feared since thousands of years or even more.

Stanford was already looking for more of those scripts as he let the light travel over the walls.

"I'm still not quite sure about that but this is not the earliest discovery at all. And we are talking about millions of years. But that is not important now. Hopefully we can find some more clues down here or even a way to defeat him. Just look closely and tell me immediately if you can see any suspicious detail."

And with that they started the investigation, all eyes on the painting without missing a single corner or even a single spot on the floor or the ceiling. During that Dipper had caught the attention of his great uncle a several times whenever he saw something strange, only to get one head-shaking after another.
Time passed and with every unsuccessful minute the frustration built up more, causing Stanford a long and tensioned sigh.

"Ah fudge! It can't be that we made all the way down here for nothing!", he grumbled and stared at the wall like it was all its fault, walked back to the other end to start from scratch, "If this is not going to help us then we-"

His voice broke up all of a sudden as he almost tripped over Dipper who was kneeling on the floor, letting out a sharp and surprised gasp and dropped the lantern before he barely managed to caught himself.

"Holy smoke!", he panted out his shock, holding onto the rock next to him as he looked down at the likewise startled boy.

"Woah! Easy there!"

"Oh god, I'm so sorry Dipper! Did I hurt you?"

"Haha, no don't worry", Dipper laughed lightly and rubbed his side,

"I already had worse, trust me."

"No, I should have watched my way, I'm sorry.

Looks like I lost my countenance for a second…"

With an excusing smile Stanford patted the kid's head and earned a slight chuckle, stepped over to his lamp which has rolled down a short path. But as he planned to pick it up his eyes got caught by the spot the light had just revealed.

"What the... Dipper! Take a look at that!", Stanford shouted and waved the kid over to him who didn't waste any second and jumped up.

Just where he stood there was a narrow gab in the wall, opened a small aisle which seemed to lead to another room. How could he had missed that prominent crack back then?

"Wow, seems like you just found a branch tunnel!", said Dipper.

"Or even a path to another cavern. A little small but maybe we can manage to reach the other side."

No sooner said than done.

With the lantern at the front the two explorers slowly crossed the wall gab like the crabs in single file, carefully pushing forward without slashing themselves open on the sharp rocks. A gaping wound was the last thing they needed in that claustrophobia trigger. But it wasn't long before Ford would stop in his motions and sway his lamp around.
A little jump and the two were standing in a small and high room, the floor almost even and hardly big enough for a king-sized bed.

"Huh… it IS a small cavern", Dipper said quietly and looked around, followed the traveling light on the walls with his eyes. "But it looks almost… arranged. Like somebody wanted to dig another tunnel or simply a hidden room."

"Yes, sort of", Ford agreed and let his fingers slide over the dusty and rough stone, his head held up. "But if that would be the case, what was that room made for? It's completely empty and the walls are all clean."

"Grunkle Ford, look over here!"

Stanford turned his head around as Dipper called him over to the other end of the room, let the light shine at the pointed out spot. At first he couldn't see anything remarkable. But as the young boy stroked the dust off the stone his eyes went wide for a second.

"What is this?..." he asked himself in curiosity and took a closer look.

Just above another ancient writing, similar to the others back in the big cave, there was an almost vanished painting of the well-known triangle with just one eye. But besides that there was nothing else around. No wheel, no black limbs attached to it, no bowing figures surrounding and no other strange symbols. And instead of the bright yellow color it had a greenish and dull shade, almost invisible on the dark stones.

"Now that is strange…" said Ford and adjusted his glasses, "A green one… haven't seen anything like this before. It looks like an added painting to the others we have seen. But why is it here all alone?"

"Maybe it's just another variation of them… or simply an older one."

"Mh… no", Ford shook his head, "No, those symbols are way too different even if they have a close resemblance. Let me see…"

After placing the lamp on the ground he grabbed inside his coat to take out the right journal for that case, scrolled to the right pages before having Dipper looking inside with him curiously.

"What does the writing say?"

"Just give me a second….", he started and read them over and used his self-made cipher key to translate the symbols as good as he can:

Omniscient Oculum Triangulum, In coelo thronum suum, Spiritus ultra et citra.

Entangulum, Cum magna voce excitantum.

Veneforis dominus ventium. Veneforis venetisarium.

"Wait a second… those phrases … they're almost the same as the incantation of Bill!"

"Huh? Really?" Dipper asked keen-eared and tried reading it by himself, "So it is just an older version of the others…"

"No no, just almost… The phrasing is a little longer than the one I know but they share a lot of identical parts. Let's… not read them out loudly yet but we definitely should take them with us."

The young boy watched his uncle confused who was putting his book back inside his pocket. He didn't really understand… was the slight difference really that important?

"But… if they have so much in common, why should they be two different incantations? That's just odd", Dipper asked after watching Ford picking up the lantern,
"I mean, I don't think that a word more or less would make such a big difference, would it? Not by someone like Bill…"

"Maybe it would, maybe not", Ford replied "But there is no time anymore for half-hearted doubts or doubled safety. This could be the clue we have been looking for Dipper, even if it looks like nothing."

"Hm… so what is on your mind?"

"Let's figure out what those words could mean in their combination and how they differ from the original incantation of Bill. Maybe we can find something like a backdoor, a recall or even a spell that can help us further."

"A magic spell against Bill… now that could be actually helpful", the kid jokingly said and gave his great uncle a slight uneasy smile.
But Ford laid his six-fingered hand on Dippers shoulder and returned that smile in a supporting manner.

"And you were the one who found it first, weren't you? Haha! Now let's get out of here. We have a long way to go."