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A 19th Century "cross written" letter. Cross writing was a technique to save paper when paper was scarce. Every scrap mattered at one time (this is dated 1823) so the writer, upon reaching the end of the page, would turn the paper 90 degrees and add a second layer of text. Once it becomes familiar, the mind adapts easily and cross written letters are surprisingly legible. Charles Darwin famously used the technique.
I have a cold, and the bandwidth is so clogged with "stay at home" shoppers, I didn't want to sit here and upload images. This is a repost from a few years ago.
Original Post from Dull Tool Dim Bulb the Daily Blog
Early 19th Century Cross Writing letter, Collection Jim Linderman