All the "dust devils" were merged and the air darkened rapidly.

The cloud of dust about them thickened.

They drew their sombreros far down over their eyes, and rode very close together.

They could not see twenty yards away, and if they became separated in the dust storm it was not likely that they would ever see each other again.

But they urged their horses on at a good rate, trusting to the instinct of the animals to take them over a safe course.
Ned had not only pulled the brim of his sombrero down over his eyes, but he reinforced it with one hand to keep from being blinded, for the time, by the sand, but it was hard work.