The historian Keith Thomas has an essay in the LRB that exemplifies the working method an “anonymous reader” describes as involving “a great many references to and citations of a generous selection of (mostly printed) texts and documents, which account for a high percentage of the text.” I could follow the same path, quoting (for instance) Thomas quoting C.G. Crump of the Public Record Office (“‘Never make a note for future use in such a form … that even you yourself will not know what it means, when you come across it some months later.’”) or Thomas quoting G.M. Young (“my aim is to go on reading until I can hear the people talking”) or Thomas quoting a Scottish friend of David Hume’s (“‘Why, mon, David read a vast deal before he set about a piece of his book; but his usual seat was the sofa, and he often wrote with his legs up; and it would have been unco’ fashious to have moved across the room when any little doubt occurred.’”), but I’ll content myself with quoting a terrifying passage quoted by Helen DeWitt, from whose paperpools post I was sent to the LRB:
It is possible to take too many notes; the task of sorting, filing and assimilating them can take for ever, so that nothing gets written. The awful warning is Lord Acton, whose enormous learning never resulted in the great work the world expected of him. An unforgettable description of Acton’s Shropshire study after his death in 1902 was given by Sir Charles Oman. There were shelves and shelves of books, many of them with pencilled notes in the margin. ‘There were pigeonholed desks and cabinets with literally thousands of compartments into each of which were sorted little white slips with references to some particular topic, so drawn up (so far as I could see) that no one but the compiler could easily make out the drift.’ And there were piles of unopened parcels of books, which kept arriving, even after his death. ‘For years apparently he had been endeavouring to keep up with everything that had been written, and to work their results into his vast thesis.’ ‘I never saw a sight,’ Oman writes, ‘that more impressed on me the vanity of human life and learning.’
For the rest (including the “omnium gatherum of materials culled from more or less everywhere”), I refer you to Thomas’s well-larded and thought-provoking essay.