During this active seedtime, Emerson was also reading in all directions. He read systematically only for a particular project. He read current books and old books…And from almost everything he read he culled phrases, details, facts, metaphors, anecdotes, witticisms, aphorisms, and ideas. He kept this energetic reading and excerpting up for over forty years; the vast system of his personal notebooks and indexes — including indexes to indexes — eventually reached 230 volumes, filling four shelves of a good-sized bookcase. The notebooks were in part his storehouse of original writing and in part a filing system, designed to store and I’ve him access to the accumulating fruits of this reading on every topic that ever interested him throughout his life.
——Robert D. Richardson Jr., Emerson: The Mind on Fire
He started with jottings, perceptions, phrases, short bits often written on the backs of envelopes or other scraps of paper, and often while out walking. Later, back in his room, he would expand the jottings in a notebook or, sometimes, a letter. Later still, he would work up a lecture or an essay, or return to a familiar subject, pulling together bits, some of which could be quite a few years old. He kept indexes for his notebooks so he could find things in what became an increasingly multivolume writer’s storehouse of material.
—Robert D. Richardson Jr., Henry Thoreau: A Life of the Mind