C. Lyell on the origin of Coal-fields. 39 
convey to the Gulf of Mexico, an equal quantity of solid matter 
in the shape of sediment, assuming the average discharge of wa- 
ter, in the great river, to be as calculated by Mr. Forshey, 450,000 
cubic feet per second, throughout the year, and the total quantity 
of mud to be as estimated by Mr. Riddell, 3,702,758,400 cubic 
feet in the year.* 
may, however, if we desire to reduce to a minimum the 
the Ghazipore average, the volume of solid matter conveyed to 
the Bay of Bengal would still amount to 20,000 millions of 
cubic feet annually. he Ganges therefore might accomplish in 
three hundred and seventy five thousand years the task which it 
would take the Mississippi, according to the data before laid 
down, upwards of two million years to achieve. 
he inducement to call attention to such calculations is the 
hope of interesting engineers in making accurate measurement 
of the quantity of water and mud discharged by such rivers as 
the Ganges, Brahmapootra, Indus, and Mississippi, and to 
Seologists to ascertain the number of cubic feet of solid matter, 
Which ancient fiuviatile formations, such as the coal-measures, 
With their associated marine strata, may contain. Sir Charles 
* See Principles of Geology, 8th ed, p.19. 
