Far off on the gray level we shall still see the antelope. His tribe is coextensive with three-fourths of the continent. No sterility discourages him. He seems as thrifty on the wiry _grama_ as among the most succulent grasses of the Republican. The sneaking coyote and a number of larger wolves put in an occasional appearance. Birds of the hawk and raven families are common. The waters swarm with numerous varieties of duck. It surprises us at this utmost distance from the maritime border to see flocks of Arctic gulls circling around the low sand-hills, and sickle-bill curlews wheeling high in air above their broods. Before we get far into this region we shall notice that one of its most typical features is the alkali-pool. Every few miles we come to a shallow basin of stagnant water saturated with salts of soda and potash. Still another characteristic of the Plains is their tremendous rainless thunder-storms. If we are fortunate enough to encounter one of these, we shall witness in one hour more atmospheric perturbation than has occurred within our whole previous experience on the Atlantic slope. The lightning for half a night will light the sky with an almost continuous glare, brighter than noonday; all the parks of artillery on earth could not make such a constant deafening roar as those iron clouds in the heaven; and though the wind will not be able to blow the train backward, as we have seen it treat a four-mule stage, it will be likely to do its next best thing, heaping sand on the track till the engine has to slow and send men ahead with shovels. Entering the Denver depot, we shall find a busy scene. All that immense freight-business between the Missouri and the Colorado mining-towns, which formerly strung the overland road with wagons drawn by six yoke of oxen each, has now been transferred to the railroad. The switches are crowded with cars getting unloaded, or waiting their turn to be. What is their freight? Rather ask what it is not. For the present, Colorado imports everything except the most perishable commodities,--and that which pays for all. If you would see _that_, ask the express-messenger on the train going East in five minutes to lift the lid of one of those heavy iron trunks in his car. Your eyes are dazzled by the yellow gleam of a king's ransom. It is a day's harvest of ingots from the stamps of Central City, on its way to square accounts with New York for the contents of one of those freight-trains.