When a visit from Dr. Tresselt, the geologist, coincides with the completion of Professor Bullfinch's latest invention, the C-Ray, Danny, Irene, and Joe are invited to go spelunking with the scientists.
Original title: Danny Dunn and the Fossil Cave
Genre: Fiction→ Children & Young Adult→ Adventure
Fiction→ Children & Young Adult→ Science Fiction→ Inventions
- Illustrated by Brinton Turkle