Read it through once

The highway that he followed was open, and at a little distance dipped into a valley, across which it could be seen running from edge to edge. He had traversed the greater part of this depression, and was climbing the western acclivity when, pausing for breath, he unconsciously looked back. Why he did so he could not say, but something seemed to impel him to the act. The tape-like surface of the road diminished in his rear as far as he could see, and as he gazed a moving spot intruded on the white vacuity of its perspective.