It will be evident, from these considerations, that the frequency of the showers, and the quantity of the rain which will fall, in the various regions respectively which the surface of the earth presents, must depend on the combined influence of many causes, such as the warmth of the climate, the proximity and the direction of mountains and of seas, the character of the prevailing winds, and the reflecting qualities of the soil.  These and other similar causes, it is found, do, in fact, produce a vast difference in the quantity of rain which falls in different regions.  In the northern part of South America, where the land is bordered on every hand by vast tropical seas, which load the hot and thirsty air with vapor, and where the mighty Cordillera of the Andes rears its icy summits to chill and precipitate the vapors again, a quantity of rain amounting to more than ten feet in perpendicular height falls in a year.  At St. Petersburg, on the other hand, the quantity thus falling in a year is but little more than one foot.  The immense deluge which pours down from the clouds in South America would, if the water were to remain where it fell, wholly submerge and inundate the country.  As it is, in flowing off through the valleys to the sea, the united torrents form the greatest river on the globe—­the Amazon; and the vegetation, stimulated by the heat, and nourished by the abundant and incessant supplies of moisture, becomes so rank, and loads the earth with such an entangled and matted mass of trunks, and stems, and twining wreaths and vines, that man is almost excluded from the scene.  The boundless forests become a vast and almost impenetrable jungle, abandoned to wild beasts, noxious reptiles, and huge and ferocious birds of prey.

Of course, the district of St. Petersburg, with its icy winter, its low and powerless sun, and its twelve inches of annual rain, must necessarily present, in all its phenomena of vegetable and animal life, a striking contrast to the exuberant prolificness of New Grenada.  It is, however, after all, not absolutely the opposite extreme.  There are certain regions on the surface of the earth that are actually rainless; and it is these which present us with the true and real contrast to the luxuriant vegetation and teeming life of the country of the Amazon.  In these rainless regions all is necessarily silence, desolation, and death.  No plant can grow; no animal can live.  Man, too, is forever and hopelessly excluded.  If the exuberant abundance of animal and vegetable life shut him out, in some measure, from regions which an excess of heat and moisture render too prolific, the total absence of them still more effectually forbids him a home in these.  They become, therefore, vast wastes of dry and barren sands in which no root can find nourishment, and of dreary rocks to which not even a lichen can cling.