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 specilic 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 
" 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 Ganr 
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 : 
t The base of the great Pyramid of Egypt covers eleven 
acres, and its perpendicular height is about 500 feet. 
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