330 
SECONDARY FORMATIONS. 
[Ch. XXIII. 
for more than 170 miles, and occupies_, it is supposed, a space 
of more than 300 miles along the coast, thus forming a surface 
of more than 25,000 square miles^ or equal to about one half 
of England *. 
Now if this modern c delta,' or, in other words, that part of 
the bed of the Atlantic which has been converted into land by 
matter deposited immediately at the river's mouth, be so 
extensive, how much larger may be the space over which the 
same kind of sediment may be distributed by the action of the 
tides and currents ! If, then, groups like the Wealden may 
be formed near the mouths of great rivers, others, like the 
lias, may be produced by the wider dispersion of similar ma- 
terials over larger submarine areas. For we may conceive that 
the Niger may carry out the remains of land plants, and the 
carcasses and bones of fluviatile reptiles, into places where they 
may be swept away by currents and afterwards mingled far 
and wide with the marine shells and corals of the Atlantic. 
The reader will remember that we stated, in the first volumef , 
that the common crocodile of the Ganges frequents both fresh 
and salt water, the same species being sometimes seen far inland, 
many hundred miles from the sea, and at the same time swarm- 
ing on the sand-banks in the salt and brackish water beyond 
the limits of the delta. 
If we are asked where the continent was placed from the 
ruins of which the Wealden strata were derived,, we are almost 
tempted to speculate on the former existence of the Atlantis 
of Plato, which may be true in geology, although fabulous as 
an historical event. We know that the present European 
lands have come into existence almost entirely since the depo- 
sition of the chalk, and the same period may have sufficed for 
the disappearance of a continent of equal magnitude, situated 
farther to the west. 
Secondary fresh-water deposits why rare. — If there were 
extensive tracts of land in the secondary period, we may pre- 
sume that there were lakes also ; yet we are not aware of any 
* Fitton's Geology of Hastings, p. 58, who cites Lander's Travels. 
■}• Page 243 ; Second Edition, p. 279. 
