Ver Beck illustrated the first publications of Chapters 7 to 12, among 14 chapters in the book. Those were 6 stories published March to August 1914 in the last six issues of The Pall Mall Magazine, v53:3-8; under no consistent general title but usually presented with "When Earth Was Young" somewhere in the header.
(Paul Bransom illustrated the same stories for their US magazine publications --all at least one month later-- and the first five of them among ch. 3-11 in Sunset under the general title "In the Morning of Time".)
The 1919 book contains only 8 illustrations, the frontispiece and 7 plates not included in the pagination. Four of the 7 plates are by Ver Beck, from the 1914 magazine stories, and legibly lettered "FRANK VER BECK". See the plates facing pp. 174, 180, 202, 220. They illustrate chapters 7-9 only.
(The other three plates appear to be not signed, not from the first UK magazine publications, and not by Paul Bransom. See those facing pp. 60, 198, 308.)