For description of the animal life of the Amazon we must turn to those works of naturalists and travellers who have made this field their special study. There we may learn about the manati, or sea-cow, one of the most remarkable of mammals, growing at times to a size of twenty feet in length, having its home in the lower and larger reaches of the river. The world of the monkeys embodies fifty species. We find them up as high as the denser parts of the Peruvian Montaña, and a colony of these creatures in conclave is always a remarkable sight, with their semi-human attributes. We shall see the sloth, and hear and see the jaguar as also the peccary. The alligator will be our constant companion amid the backwaters, and a dangerous and voracious one at times he proves. The turtles may furnish the traveller with its flesh and eggs for food, as it has done for the Indians always. The traveller on occasion need not despise, moreover, the flesh of the monkey, however repugnant it may seem in life to contemplate the creature as a constituent of the forest larder. The mighty boa-constrictor will be seen by the fortunate. The brilliant plumage of the many-hued birds is perhaps a compensation of Nature for the lack of song of the many feathered tribes of the valley. As for the parasitic creatures, the ticks, the dreadful ants and a host of others, the traveller here will rarely fail to make their close acquaintance. The western or upper edge of the Amazon Valley differs much from the denser region such as that to which the foregoing description regarding the forest applies, conditions obtaining more particularly in the Brazilian portion of the territory. This upper edge--extending, however, in some cases a long way to the east--is known in Peru as the Montaña, and embodies a much more broken and diversified landscape, more beautiful and more habitable. Bolivia, Colombia and Venezuela also partake in territory of this character, which is formed by the slopes of the Andes. As the traveller descends the eastern slopes of the Cordillera, whose tablelands and ridges we have traversed in a previous chapter, and leaves behind him the vast grass-covered uplands, with their towering peaks, he enters upon the line of tree-life, which lies at an elevation of perhaps 11,000 feet: enters indeed upon another world. The climate becomes warmer, the mists lie heavier, thickets of flowering shrubs spread their beauty, cascades of falling water are projected like giant fountains over sheer precipices, and timber-clad ridge and profound cañon, between whose walls the torrential rivers now hurry eastwards, diversify the journey; transformation scenes which delight the eye and give an added zest to the arduous march.