It's a collection of nursery rhymes. What else do you really need to know?
There's a good handful of the more popular Mother Goose rhymes in this book - Humpty Dumpty, Little Bo Peep, Ba Ba Blacksheep, Hey Diddle Diddle - but most of the rhymes are the ones that never got much repetition. Probably because some of them are several pages long, and you've got to twist them around in your mouth to make the rhyming feel like it's fluid.
And there's some Lewis Carroll thrown in there for some reason.
The illustrations are a lot of fun. There were something like four or five different artists who did the pictures for this book, and each one brings their own style.
There were a lot of pictures of dogs in waistcoats.
And demon sheep.
I'll stop now, or this will end up being nothing but pictures.
You can read it at the Project Gutenberg