The boys looked and saw the imprint of a foot!
Yet, on inspection, it was unlike a human foot and seemed more like the track of a bear. Several other prints of a similar nature became visible now that they examined the spongy soil carefully.
"Whatever do you think it is?" Frank asked of the professor, who was examining the imprints with some care.
"I don't know, my dear boy," he replied. "It looks like the foot of a bear, and yet it appears to be webbed as if it might be that of some huge water animal."
"Yes, but look at the size of it," argued Billy. "Why, the animal whose foot that is must be an immense creature."
"It's certainly strange," mused the professor, "and suggests to me that we had better be getting back to our aeroplane."
"You think it is dangerous to remain here, then?" asked Harry, with some dismay.
"I do, yes," was the naturalist's prompt reply. "I do not know what manner of animal it can be that left that track, and I know the tracks of every known species of mammal."
"Perhaps some hitherto unknown creature made it," suggested Billy.
"That's just what I think, my boy," was the reply. "I have, as I said, not the remotest conception of what sort of a creature it could be, but I have an idea from the size of that track that it must be the imprint of a most formidable brute."