“Darker? Couldn’t be.”
Then, as Bob gazed ahead at the opposite slope, he uttered an exclamation of bewilderment.
“It is getting darker!” he cried. “Why—why, it’s impossible. Dark at nine in the morning! Something’s wrong somewhere!”
A second later Mr. Holton rode up to the boys anxiously.
“Get out your goggles!” he directed them. “We seem to be riding into a fog of black dust. Tishmak thinks we may have to stop for the day.”
CHAPTER XV
As Guests of Heathens
“WHAT!” cried Bob excitedly. “Stop for the day! We—we can’t. Our time is worth too much!”
The naturalist laughed unwillingly.