You can read his works at Archive.org

This gem of a site has a massive collection of books that you have heard about but are no longer available. One of the features are links to books that have been converted to audio via LibriVox. Many sessions while on a treadmill I have filled in my time listening to Boston Blackie or the Art of War.
Take advantage of this site to actually read Tarzan of the Apes (and the subsequent editions) as well as compare John Carter of Mars with the original texts.