1 
320 _ ELEMENTS OF GEOLOGY. 
shown, when treating of the Mississippi, that a more ancient 
delta, including species of shells such as now inhabit Loui¬ 
siana, has been upraised, and made to occupy a wide geo¬ 
graphical area, while a newer delta is forming and the pos¬ 
sibility of such movements and their effects must not be lost 
sight of when we speculate on the origin of the Wealden. 
It may be asked where the continent was placed, from the 
ruins of which the Wealden strata were derived, and by the 
drainage of which a great river was fed. If the Wealden was 
gradually going downward 1000 feet or more perpendicu¬ 
larly, a large body of fresh water would not continue to be 
poured into the sea at the same point. The adjoining land, 
if it participated in the movement, could not escape being . 
submerged. But we may suppose such land to have been 
stationary, or even undergoing contemporaneous slow up¬ 
heaval. There may have been an ascending movement in 
one region, and a descending one in a contiguous parallel 
zone of country. But even if that were the case, it is clear 
that finally an extensive depression took place in that part 
of Europe where the deep sea of the Cretaceous period was 
afterwards brought in. 
Thickness of the Wealden, —In the Weald area itself, be¬ 
tween the North and South Downs, fresh-water beds to the 
thickness of 1600 feet are known, the base not being reached. 
Probably the thickness of the whole Wealden series, as seen 
in Swanage Bay, can not be estimated as less than 2000 feet. 
Wealden Flora, —The flora of the Wealden is characterized 
by a great abundance of Coniferae, Cycadese, and Ferns, and 
by the absence of leaves and fruits of dicotyledonous angi- 
osperms. The discovery in 1855, in the Hastings beds of the 
Isle of Wight, of Gyrogonites,'or spore-vessels of the Chara, 
was the first example of that genus of plants, so common in 
the Tertiary strata, being found in a Secondary or Mesozoic 
rock. 
* See above, p. 102; and Second Visit to the United States, vol. ii., chap, 
xxxiv. 
