6 
Mississippi. Sir C. Lyell, from the present amount of solid 
matter conveyed by it, and the area and depth of the accumula- 
tion near its mouth, inferred that 67,000 years would be needed 
for the Delta proper, and 33,000 more for the plain above to 
be transported to its present site. Hence he speaks of the 
whole period as “ perhaps far exceeding 100,000 years.” But 
in 1869 he says that “ the data had considerably altered since 
first he wrote. Becent calculations had doubled the volume 
of water flowing into the sea, and thus the same effect might 
be produced in half the time previously calculated.” Thus 
50,000 years were struck off by the first correction. 
But now let us assume, instead of a fixed annual amount 
of detritus, that there has been a steady decrease of only one 
four hundredth part of the present quantity. The 50,000 
years would then reduce themselves to 5,937, which would 
bring the commencement of the process within the limits of 
the known or biblical age of mankind. 
8. Again, Mr. Croll makes a calculation, that the same river 
at its present rate would carry down the whole area drained 
by it to the sea-level in 4^ million years. But, adopting a 
similar law, or supposing the decrease each year to be only 
one part in a thousand of the present amount, how long 
would have been needed to waste away a double quantity of 
land or rock to its present amount ? Bather less than 94,000 
years. 
The same principle applies to the mud of the Nile, and a. 
vast number of cases of a similar kind. The doctrine of 
averages, when so applied, rests on a mere assumption, not 
only unproved, but highly improbable, and almost certainly 
untrue. In a single year of high flood a river may transport 
an amount and kind of material, which could not have been 
removed by a hundred years in which no flooding has 
occurred. 
9. The case is the same as to upheaval and volcanic 
eruptions. It is plain that whenever the crust is broken 
through, and a stream of lava, before pent in, comes from 
below, the motive force must tend to exhaust itself by the 
effort. The heat, generated by internal pressure, will partly 
escape through the opening, while the pressure also is 
lessened by the rupture of the crust. The approach must bo 
constantly towards a limit, when the upward and expansivo 
force has spent itsolf, and though the renewal may have gone 
on through long ages, the first intensity or amount of action 
can never return. The process of condensation, with the 
generation of internal heat, and its conflict with the cooling 
ocean at the surface, or the intense cold of the interstellar 
