SEDIMENT IN RIVERS. 



157 



of Egypt, if it were a solid mass of granite, would 

 weigh about 6,000,000 tons. The mass of matter, 

 therefore, carried down annually, would, according 

 to this estimate, more than equal in weight and 

 bulk 42 of the great pyramids of Egypt, and that 

 borne down in the four months of the rains would 

 equal 40 pyramids. But if, without any conjecture 

 as to what may have been the specific gravity of 

 the mud, we attend merely to the weight of solid 

 matter actually proved by Mr. Everest to have been 

 contained in the water, we find that the number of 

 tons' weight which passed down in the 122 days of 

 the rainy season was 339,413,760, which would give 

 the weight of 56 pyramids and a half; and in the 

 whole year, 355,361,464 tons, or nearly the weight 

 of sixty pyramids."* Mr. Lyell farther states, that 

 I if a fleet of more than 80 Indiamen, each freighted 

 with 1400 tons' weight of mud, were to sail down 

 the river every hour of every day and night for 

 four months continuously, they would only trans- 

 port from the higher country to the sea a mass of 

 solid matter equal to that borne down by the Gan- 

 ges in the flood season ; as the exertions of a fleet 

 of about 2000 such ships going down daily with the 

 same burden, and discharging it into the gulf, 

 would be no more than equivalent to the operations 

 of the great river. Yet, in addition to this, it is 

 probable that the Burrampooter conveys annually 

 as much solid matter to the sea as the Ganges " 



Deltas. 



A delta is a deposite of earthy matter, generally 

 at the mouths of rivers, and is so called from its 

 resemblance to the Greek letter A, which may be 

 represented thus : 



* The base of the great Pyramid of Egypt covers eleven 

 acres, and its perpendicular height is about 500 feet. 



