8 THE RUBBER INDUSTRY 



an important factor in the lumber industry of the 

 world. It is in these forests that the many varieties 

 of rubber-yielding trees are found, but no accurate 

 information as to the number is available. There is 

 not the smallest doubt that the total runs into hun- 

 dreds of millions, and for practical purposes may be 

 considered inexhaustible ; but the supply of latex for 

 the manufacture of rubber for export is controlled by 

 the lack of any large labouring population, and by the 

 cost of collection and carriage to the river-banks for 

 transport to any commercial market. 



One most remarkable fact in connection with the 

 waterways of the Amazon Valley is the very insignifi- 

 cant gradient of the rivers. The fall seldom exceeds 

 10 feet in 100 miles. The difference between sea-level 

 on the Atlantic coast and Iquitos, 2,400 miles inland, 

 is less than 200 feet, or approximately 0*0000015 P er 

 cent. In spite of this very slight difference in levels, 

 the average current in the main river and its tributaries 

 in normal seasons is at the rate of four miles an hour, 

 increasing to a noticeable degree in times of flood. 

 This strong current is accounted for by the discharge 

 of water from the melting of the snow in the Andine 

 ranges, and the enormous accumulations of rain-water 

 in the basin through which the upper rivers take their 

 course. 



The melting of the snow in the Cordillera of the 

 Andes and the heaviest rainfall take place con- 

 currently during a period extending from the middle 

 of November to the end of March in each twelve 

 months, and it is then that the volume of water in 

 the river channels attains its maximum height. The 



