1) You'll find the scroll in the north-eastern part of the Black Stone, in the present, right after using a time portal and landing on a small balcony.
Directions: E N E N S
2) The scroll lies in the western part of the Black Stone. Make sure you're in the present and activate two portals to get through to the north room. Approach the symbols painted on the wall to unlock the secret automatically.
Directions: W E N S W