Primary Sources are written accounts by first-hand observers, and any relevant documents from the very same era. For Maine's early past, examples would be Christopher Levett's (1624) A Voyage Into New England, and (if preserved) any business records from his travels and trading-post in now-Portland-Harbor ME. The relative accuracy & bias of Primary Sources have to be assessed & taken into account by the scholars who use them. (Levett's book is usually given favorable ratings.) Secondary Sources are second-hand written accounts, either from the same time as the events described (such as Purchas' published account from Hakluyt's papers, titled Description of the Countrey of Mawooshen), or from a later time's scholarly analysis of Primary Sources (like Williamson's 1832 History Of The State Of Maine, which provides footnoted references to his Primary Sources of information - so that others may check-up on their accuracy, as scientists should do). Tertiary Sources, although not an official term, nonetheless usefully designate much-later, &/or less-scholarly, written summary-accounts - perhaps intended only to tell a good story, not to preserve facts. A relevant example of this sort for us to be wary of is Sebago Lake Land In History, Legend & Romance by Herbert G Jones (1946), because it is still widely used as an information-source today, but does not clearly distinguish what is History and what is Legend & Romance, nor tell where Jones got his data from, nor even distinguish genuine Native American legends from Euramerican romance about Indians. (Indians need no enemies with friends like this.)