[epilys]

I recommend the 1621 book Anatomy of Melancholy by Robert Burton. He was a big bibliophile with a huge collection, and also melancholic, so he wrote about melancholy while pulling material from his own reading. The result is a huge book that is figuratively 50% main text and 50% marginalia; if you find a good edition where they are printed as actual marginalia instead of footnotes/endnotes, it gives a completely different perspective into the mind of the author as he wrote the book.

[billfruit]

Also Montaignes Essays also makes a large book with his musings on his life including his vast reading.