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NATURALIST'S GUIDE TO THE AMERICAS 



36.63°C., minimum 14.43°C. (4 years of 

 records) with a difference of only 2.25°C. 

 between the coldest (June) and the 

 hottest month (September). At Rur- 

 renabaque, Bolivia, on the Beni river 

 and at the base of the last Andean spur, 

 at an altitude of about 1000 ft., the 

 average temperature is said to be around 

 25°C. Higher up at Huanaco, Peru, 

 altitude 6270 ft., the average annual 

 temperature is about 24°C., while at 

 Iquitos, Peru, lower down, the tem- 

 perature is higher. The campos regions 

 north of the Amazon are said to be more 

 temperate than the main river valley. 

 The records and opinions of many travel- 

 lers (among them A. R. Wallace) show 

 the climate of the Amazon valley, for 

 the most part, to be a relatively pleasant 

 one, as far as the temperature is con- 

 cerned, its chief disagreeable quality 

 being its everlasting, enervating same- 

 ness. 



In many parts of this region, winds of 

 various kinds modify the temperature 

 markedly. During the dry season, the 

 prevailing winds on the lower Amazon 

 (below Manaos) are from the north and 

 east ("vente geral"), while the "vente 

 de cima" from the west and southwest 

 prevails during the rainy season. At 

 times, particularly in the dry months, 

 a night breeze the "terral" hovers over 

 the river. In the upper river region 

 embracing the country between the 

 Beni and Mamore on the south and the 

 upper Rio Negro on the north as far 

 east as Manaos, very sudden changes in 

 temperature are caused by the "sur" 

 (Beni) or "friagem" (Purus river re- 

 gion), a strong cold wind that blows 

 spasmodically between March and June 

 from the southwest. A drop of tem- 

 perature from 33° to 11°C. in a few hours 

 at about 520 ft. altitude has been re- 

 corded from northeastern Bolivia. Ac- 

 curate detailed climatic data are lacking 

 for many of the areas immediately 

 adjacent to the east Andean ranges. 

 Even during the dry season, there are 

 regions here that are saturated with 

 moisture, such as the Yungas in Bolivia 

 and the tops of many mountain ridges. 



In July and September, in such regions, 

 almost everything is moisture-laden 

 and embowered in damp moss and 

 lichens. 



II. ORIGINAL BIOTA 



1. Vegetation and large animals 



Heavy forests that for unbroken ex- 

 tent and diversity of vegetation types 

 are nowhere equalled in the world, 

 border the main river and its principal 

 tributaries, extending far up the eastern 

 flanks of the Andes, where they are 

 gradually replaced by the shrub or 

 chaparral (ceja) formations which con- 

 tinue the zone of woody plants to about 

 10,000 to 12,000 ft. altitude, the last 

 remnants confining themselves closely 

 to the stream beds, deep down in the 

 canon-like valleys. For 2000 to 4000 

 ft. above this woody plant limit, the 

 slopes are occupied by herbaceous tem- 

 perate types. Higher still is a scanty 

 vegetation, largely grasses and alpines, 

 the latter closely appressed to the 

 ground and only occurring in favorable 

 situations, such as sheltered springs. 

 The "campos" regions (pampas, pajo- 

 nales, savannas) between the main 

 tributaries and in the vicinity of the 

 headwaters of many of the affluents are 

 rather high prairies, often monotonously 

 flat with marshy depressions (enriches) 

 through which very sluggish streams 

 act as drainage canals. Some of the 

 "campos" regions are hilly, rolling and 

 comparatively dry, such as the Campos 

 Geraes (Brazilian Guiana), while others 

 such as the Campos Mojos, in north- 

 eastern Bolivia, are rather wet even 

 before the rainy season begins. Be- 

 tween the pure prairies and the forests 

 (monte, montana) is a park-like country 

 of prairies sprinkled singly with trees, 

 and with islands of woody vegetation 

 (ihlas de mato) varying in size from a 

 square rod or so up to 5 to 10 acres. 

 Between the forests and the low water 

 line, particularly on the upper Amazon 

 and on most of the southern tributaries, 

 but not on the Rio Negro and other 

 "black water" rivers, there are often 

 areas dominated largely by the huge 



