Illustration from The 12 Dancing Princesses
Date of Copy
This is by Kay Nielsen, an iconic Danish illustrator who is especially known for his fairy tale illustrations. In addition to working on many children's books, he did concept art for Disney back in their early days.
He used a lot of long, elegant shapes, swirling lines, and dense but delicate patterns. In the fantastical visual worlds he creates, fairy tale logic doesn't seem so far fetched.
Reading his Wikipedia entry, I was a little bummed out to see that after a period of success, he died in poverty with his work out of fashion. I'm glad he's been rediscovered and is now beloved by many people. There's more excellent information about Kay Nielsen at Terri Windling's blog.
Reference image from this online gallery. It was originally published in the story collection "In Powder and Crinoline".