M.C. Burkitt, "Prehistory", 2nd ed. (Cambridge, 1925)

In their The J.R.R. Tolkien Companion & Guide, rev. & exp. ed. (HarperCollins, 2017), Christina Scull and Wayne Hammond write (p. 492):

"The page illustrating some of the cave paintings found by Father Christmas, Polar Bear, and Cave-Bear which accompanied Tolkien’s 1932 *‘Father Christmas’ letter was based on real examples in Europe.... [W]e have been informed by *Christopher Tolkien that all of the ‘Father Christmas’ cave images appear in a book which had once belonged to his father, Prehistory: A Study of Early Cultures in Europe and the Mediterranean Basin by M.C. Burkitt (2nd edn. 1925)."

I recently obtained a copy of this work, in dust-jacket, and thought folks here might like to see some photos of (and from) it.

A scanned copy of the volume can be found on the Internet Archive site here:

https://archive.org/details/cu31924029918699

You can see some of the original rock carvings from which these various drawings were made — including the ultimate origin of Tolkien's drasil-riding goblins (see below) — in situ here:

https://www.tanumworldheritage.se/besoksmal/litsleby-rock-carvings/