28 Physical Geography of the Amazons Valley. [January, 
some of the differences between the two regions. Following him 
in part we may thus divide them: 
1. The Upper Amazons region, to the base of the Andes and 
for hundreds of miles on both sides of the river, is a perfectly 
level expanse, nowhere raised more than a hundred and fifty feet 
above the river and generally only just out of reach of the high- 
est floods. The Lower Amazons, on the contrary, passes through 
a comparatively high country, with table-lands several hundred 
feet above the river and many abrupt hills or even mountains. 
These elevations increase towards the north and south until they 
join the great table-lands of Guiana and Brazil. 
2. As a consequence the great tributaries of the Upper Ama- 
zons—notably the Purts, Juruá and Içá—present a perfectly open 
navigation almost to their sources ; but those of the Lower Ama- 
zons are obstructed by rapids and falls where the water flows 
down from the highlands. A secondary consequence is that the 
Upper Amazonian branches are very crooked, while those of the 
Lower Amazons are comparatively straight. 
3- The soil of the Upper Amazons is either a rich ferruginous 
clay or vegetable mold which, according to Bates, often attains a 
thickness of twenty or thirty feet; stones are hardly ever met 
with. On the Lower Amazons the soil is nearly always sandy, 
and mold forms only in favored localities, such as swamps and 
river-banks, 
4. On the Upper Amazons the trade-wind is never felt, and the 
air is always moist and warm; rains are very frequent, especially 
near the Andes, and the dry season is only marked by the com- 
parative lightness of the daily showers. On the Lower Amazons 
the trade-winds blow freely during a great part of the year, and 
there is a well-marked dry season; in some districts the rains 
cease almost entirely for weeks together. Probably the average 
temperature is somewhat lower near the Atlantic than on the Up- 
per Amazons. : 
5. The great forest of the Upper Amazons, so far as we know, 
is unbroken except by the rivers, and it has a width of a thou- 
sand miles or more from north to south. The forest belt of the 
Lower Amazons is hardly half so wide, and it is interrupted in 
many places by campos or open lands, either grassy or stony 
plains, without trees, or sandy tracks with a thin semi-forest 
growth like that of Central Brazil. 
