“Exactly,” the professor agreed, “like the giraffe-camels. But in later deposits, the types mixed. Now, Perry, if you think you really want to come with me, you can either join me in three weeks at the Museum Camp near Haystack Butte, or you can join me a few days earlier and go with me to the Loup River formation in Nebraska. It’s on the way, and the Museum received a letter the other day from a ranchman, who seems to have found a fine specimen of the Columbian mammoth. They want me to go and look it over. I thought you might like to see a mammoth embedded. As I understand, this chap has had the sense to leave the skeleton untouched, so it may be in good shape.”
“I’d awfully like to go there,” said the boy, “but I do think I ought to finish up the Pteranodon first, and it’ll take me all of two weeks. I’ll join you out at Haystack Butte, if I may. I’d like to go with you to see that mammoth, though, ’cause I’ve never seen one really in the ground. And just what sort of a beast was the Columbian Mammoth, Uncle George? I’ve never got clearly in my head the differences between a mastodon and a mammoth.”
“It’s a thing you ought to know,” his uncle said, “particularly as you found the Moeritherium for us. You remember the Paleo-mastodon skull that Antoine found the night before you made your discovery, don’t you?”
“Of course!”
“And you remember that while the Moeritherium skull was found in an Upper Eocene bed, the Paleo-mastodon skull was found in a lower Oligocene.”
“Of course.”
“And you just now told me that Africa was an island during the Eocene period and that it gradually rose, making land bridges across the Mediterranean during the later Oligocene.”
“Yes,” Perry agreed.
“Very good. Then, when the land bridges were made, and the mammals from Africa first had the chance to make their way into Europe and Asia and so on to America, the ancestors of the elephants were a little more advanced than Paleo-mastodon. That’s clear?”
“Quite.”