Here is how Dickens described his visit to the plains west of St. Louis.
"Looking toward the setting sun, there lay, stretched out before my view, a vast expanse of level ground; unbroken save by one thin line of trees, which scarcely amounted to a scratch upon the great blank; until it met the glowing sky, wherein it seemed to dip: mingling its rich colors, and mellowing in its distant blue... It was lonely and wild, but oppressive in its barren monotony. I felt that in traversing the Prairies, I could never abandon myself to the scene, forgetful of all else; as I should do instinctively, were the heather underneath my feet, or an iron-bound coast beyond; but should often glance towards the distant and frequently receding line of the horizon, and wish it gained and passed."
The vast expanses of the Plains often had a disconcerting effect upon Europeans, and Dickens clearly is a member of that fraternity. Many saw the Plains as like being in a punch bowl where the horizon at the same time receded in one's direction of travel and followed behind.