XI. 
THE GREAT CENTRAL VALE. 
External Configuration and Internal Structure. — Were the 
general level of the land in the north of England to be lowered only 
100 feet, (a case quite familiar in reasoning concerning ancient geolo- 
gical phenomena,) the great vale of York would be submerged; the 
Tees, Swale, Yore, Wisk, Nidd, Wharfe, Derwent, Aire, Calder, Dun, 
Trent, and Hull, would separately reach the sea, and powerful currents 
flowing up and down what is now the vale of York would occasion in 
it changes of the most important kind. By some such combination in 
earlier eras of the world, the phenomena visible in this great hollow, 
which extends from the Tees to the Trent, and by that river is united 
to the parallel broad plains of Nottinghamshire, and the central parts of 
England, were probably occasioned. 
The strata visible at particular points in the vale of York are red 
sandstone, (Boroughbridge,) red clays and gypsum, (Howsham,) blue 
lias clays, (Topclifie) ; and under all these runs the magnesian limestone 
in a continuous low terrace, dividing the vale of York from the Western 
regions already described. The greater part of the vast area under 
which the red formation spreads, is covered superficially and to a consi- 
derable depth by gravel, clay with pebbles, and small accumulations of 
lacustrine marls. Anciently many small lakes have existed in the vale 
of York, but drainage and vegetable growth have obliterated nearly all. 
Aspect of Vegetation.-— Receiving from numerous streams the 
detritus of the uplands lying east and west, the vale of York is full of 
plants which seem derived from these districts, as well as others more 
commonly found in lower ground. Its flora is consequently very rich, 
and plants supposed to characterize different soils grow here near 
together. 
DISTRIBUTION OF PARTICULAR PLANTS. 
The following species of plants have been found in no other district 
of Yorkshire. 
Viola lactea 
Peplis portTila 
Cnicus pratensis 
Symphytum officinale 
Lysimachia thyrsifiora 
Hottonia palustris 
Samolus Valerandi 
Scheuclizeria palustris 
Tulipa sylvestris 
