In this valley, among the Cordilleras, three great rivers--the Orinoco, the Amazon and La Plata--rise. The mountain ranges north and south of the Amazon divide this great valley into three lesser valleys, down which the Orinoco, the Amazon and La Plata flow, watering three-fourths of South America. _The Orinoco_. The headwaters of the Orinoco rise in two ranges of mountains; the Cordilleras in the west, and the mountains of Venezuela many hundred miles to the east. Four hundred tributaries, abounding in beautiful falls and cataracts, unite to form this great river. The whole valley for 1600 miles is filled with dense and tangled forests. Noble trees of unrivalled beauty blossom in endless prodigality. Birds of gorgeous plumage nestle in their lofty recesses. Tall ferns, vines, creeping plants and parasites form a dense tangle of undergrowth, swarming with life. Myriads of insects in great variety, reptiles of strange and singular form, lizards and venemous serpents find their homes and sustenance in the wild, dense mass of vegetation. _The Amazon_. The valley of the Amazon collects its waters from a region 1800 miles wide from north to south and 2500 miles long from the Andes to the Atlantic ocean. Even at the foot of the Andes the Amazon is a mighty river. The valley rapidly narrows to a width of 600 or 700 miles, and then more gradually to the ocean, {4} where it is only 150 miles wide. Its total fall from the foot-hills of the Andes to the Atlantic is very slight, not over three or four hundred feet, and probably considerably less. The rims of the valley are formed of diorite and sandstone, and are raised only a little above the flood-plain, which is formed of mud and silt, the detritus brought down by the Amazon and its tributaries. The flood-plain is from fifty to one hundred miles wide, gradually narrowing as it approaches the ocean. Through this valley the Amazon cuts its way, separating often into channels which sometimes run parallel to each other for several hundred miles, frequently forming large islands, or expanding into lakes. Similar flood-plains are found on all its larger tributaries. Up from the ocean into this valley an immense tidal wave rolls, with a bore, twice a day, forcing back the current of the Amazon 500 miles and inundating a portion of the flood-plain.