In about two hours the professor returned, having collected a number of specimens and escaped getting into any difficulties or dangers for once.
"We'd better start," he called. "I'm anxious to get to that underground city. If that turns out half as well as I expect, our fortunes are made."
"Will it be better than the gold mine?" asked Bob, with a grin.
"The gold mine!" exclaimed the naturalist. "Why, I had rather reach this buried city than have half a dozen gold mines!"
He was very enthusiastic and seemed anxious to get on with the journey. The automobile was made ready, and, bidding their hosts good-by, the travelers were again under way.
As they progressed the road became rougher and more difficult of passage. In places it was so narrow that the automobile could barely be taken past the thick growth of foliage on either side.
The forest fairly teemed with animal life, while the flitting of brilliantly colored birds through the trees made the woods look as if a rainbow had burst and fallen from the sky. Parrots and macaws, gay in their vari-tinted plumage, called shrilly as the puffing auto invaded their domains.
It was necessary to run the car slowly. The professor fretted at the lack of speed, but nothing could be done about it, and, as Jerry said, it was better to be slow and sure. So they went on for several miles.
About noon the travelers came to the edge of a broad river, which cut in two the road they had been following.
"Here's a problem," said Jerry, bringing the car to a stop. "How are we going to get over that? No bridge and no ferry in sight."
"Perhaps it isn't as deep as it looks," suggested the professor.
"Tell you what!" exclaimed Ned. "We'll all go in for a swim and then we can tell whether it's too deep to run the auto across."
His plan was voted a good one, and soon the boys and Professor Snodgrass were splashing about in the water. Their bath was a refreshing one. Incidentally, Ned found out that he could wade across, the stream in one place coming only to his knees, while the bottom was of firm sand.
While the travelers were splashing about in the cool water, they might not have felt so unconcerned had they been able to look through the thick screen of foliage on the bank of the stream, and see what was taking place there.