EVIDENCE OF FOSSIL REMAINS 87 



year. From these figures the amount of materials in 

 suspension discharged into the Gulf of Mexico becomes 

 known. It is sufficient to cover one square mile to the 

 depth of 269 feet ; in twenty years it is one cubic mile, 

 or five cubic miles in a century. Turning now to the 

 other aspect of this process, and the antecedent causes 

 which produce these effects, it appears that the area of 

 the Mississippi River basin is 1,147,000 square miles — 

 about one third of the total area of the United States. 

 Knowing this, and the annual waste from its surface, it 

 is easy to demonstrate that it will take 6000 years to 

 plane off an average of one foot of soil and rock from 

 the whole of this immense area. Of course only an 

 inch or a few inches will be taken from some regions 

 where the ground is harder or rockier, or where little 

 rain falls, while many feet will be washed away from 

 other places. The waters of the Hoang-ho come from 

 about 700,000 square miles of country, from which one 

 foot of soil is washed away in 1464 years. The Ganges 

 River, draining about 143,000 square miles, carries off 

 a similar depth of eroded materials from its basin in 

 823 years ! Should we add to the above figures those 

 that specify the bulk of the chemical substances in 

 solution carried by these waters, the total would be 

 even greater. We know that in the case of the Thames 

 River, calcareous substances to the amount of 10,000 

 tons a year are carried past London, and all this mineral 

 has been dissolved by rain-water from the chalky cliffs 

 and uplands of England, so that the land has become 

 less by this amount. Thus we learn that vast altera- 

 tions are being made in the structure of great continents 

 by rain and rivers, as well as by glaciers and other 



