The Tablets of Dagon

"'These are the Tablets of Dagon... this must be the original source text for Obed's translation, the Book of Dagon.' (Jack Walters)"

Overview
The Tablets of Dagon are a set of relics, presumably granted to the Deep Ones by their Father itself. They are held within the city of Y'ha-nthlei in the Temple of Dagon, their studying having become Robert Marsh's obsession. The Tablets seem to have been around since centuries, possibly millennia, as Robert mentions that his great-grandfather, Obed Marsh himself, started their translation back in his day.

Role in the game
They are found by detective Jack Walters near the end of the game, who manages to finish translating them.

Contents :
The following is taken directly from Jack's journal:"'These ancient tablets are written in the strange glyphs of the Deep Ones, they include the final passages that are missing from the translations in the Book of Dagon.""They seem to be a prophecy ; further study would be needed to produce an exact translation, but the passage reads roughly as follows :"" 'And the time shall come when the stars are right, and lo, we shall raise up that which has been sunken.""So shall lost R'lyeh be lifted from the deep, and the waters shall recede from it's palaces.""And the One Who Dreams shall be awakened, Great Cthulhu shall arise ;""And fear and madness shall be upon the face of the world.''"

Link to the Cthulhu Mythos :
These tablets are yet another hint of Cthulhu's prophesied return upon the world, which shall bring about the end of mankind. The final passages also seem to echo a certain incantation chanted by Cthulhu's faithful : "In his house at R'lyeh dead Cthulhu lies dreaming..."

They are also further proof (if needed) of the link between Dagon and Great Cthulhu itself.

Trivia :

 * Interestingly in the RPG, the Tablets of Dagon are a set of five conical stones while in the video game, they are two actual tablets. They are however in both versions covered with glyphs of R'lyeh as well as the original text of the Book of Dagon.