Why is Mr. Pyncheon so desperate to find the lost deed or parchment to land east of Pyncheon house?

Mr. Pyncheon brings up a claim that the Pyncheon family has on an Eastern tract of land. He tells Maule that Colonel Pyncheon had a deed to this land that has since disappeared. Mr. Pyncheon suspects that the disappearance of this deed had something to do with the Maule family, and there is an ordinary saying that Maule took miles and miles of the Pyncheon land to his grave. Mr. Pyncheon theorizes that Maule's father took the deeds when he was working for Colonel Pyncheon on the day before the Colonel died.