THE INVISIBLE MENACE At the close of the second day the big trail herd halted at the edge of the vast level over which it had come.

The herd had been driven forty miles.

Cattle, men, and horses had passed through a country which was familiar to them; a country featured by long grama grass, greasewood, and cactus plants.
There was no timber on the plains.

The gray of the grama grass and the bare stretches of alkali shone white in the glare of a sun that swam in a cloudless sky of deepest azure.

Except for the men, the cattle, the horses, and the two slow-moving, awkward-looking canvas-covered wagons, there had been no evidence of life on the great plain.