Monday Cartoon Day.
The way Al Jaffee tells it, his daily panel Tall Tales, which started in 1959, went wrong when his editors at the syndicate paper insisted he started adding dialogue to what was essentially a silent panel (in a weird and chalanging shape). This meant he lost most of his foreign sales, which made the panel unrewarding to do. Here is a large selection of Tal Tales panels from the earliest to the last perion. There are text gags in between, but you can really see the change toward the end in 1964.