An article on “The Literature of Friendship” in The North American Review mentions Thoreau, along with many other notable literary figures:

But perhaps the worthiest paper on the subject is contained in the “Wednesday” of Thoreau’s “Week on the Concord and Merrimack Rivers,”—a composition which every one enamored of the theme should reperuse and ponder. “Friendship is evanescent in every man’s experience, and remembered like heat-lightning in past summers.” “Of what use is the friendliest disposition, if no hours are given to friendship?”