558 TRANSACTIONS OF SECTION E. 
of the adjacent Cotswolds; but here all three are more complex—(a) the 
flowing water is not confined to the surface but permeates (c), which rises 
in steep banks above the irregular (6) flood-plains and forms a gently undulating 
and sloping surface very different from that of (c) in the Plain. Further, 
while the varieties of (c) in the Plain are mainly 7. clay and i. gravel-capped 
clay, the varieties of (c) in the Cotswolds are (a) the relatively flat land, 
i. very fertile cornbrash, ii. less fertile belts of Oolitic limestone, wii. cappings 
of gravel, iv. cappings of clay and (8) the steep slopes 7. of the valleys, and 
vi. of the escarpment. There are also considerable differences in climate 
differentiating the Plain from the Scarped Ridges, and the climatic conditions 
within the natural region itself vary much more in the hilly region than they 
do in the plain. The Upper Thames Vale is, then, clearly a different natural 
region from the Cotswold Scarped Ridge. There are, however, vales and vales, 
scarped ridges and scarped ridges. The Upper Thames Vale is a much simpler 
variety of the same species of natural region than the Vale of Aylesbury, and 
the chalk-scarped ridges are a variety of the species differing from the oolitic 
limestone variety. 
This grouping according to orographical conditions has its advantages, but 
others suggest themselves—more particularly the division into regions with a 
common drainage, e.g. the basins of Cherwell, Evenlode, Windrush, &c. 
Probably it is best to combine the two and see in the Cotswolds each incised 
river-valley as a sub-division of the natural region and the relatively flat land 
between as another sub-division. In plains the land between the rivers becomes 
by far the largest and most important sub-division. 
We might look on the geological structure as the tissue of a region; but this 
geological structure does not suffice for a complete natural region. The water 
circulation must also be taken into account and the surface forms it has carved. 
In a mountainous area the valleys seem the natural units, divided by crests; in 
the plains the land between the rivers is the dominant element, and the rivers 
divide the natural regions. There are many intermediate forms between these 
extremes of mountain and plain, of which the Cotswolds are a good example. 
Individual valleys, plateaus, and plains form simple “geographical units.? 
Groups of different varieties of one or more of these constitute a new and more 
complex geographical order. These in their turn may be combined to form 
something more complex, such as the English Scarplands, the Welsh Highlands, 
&c. Yet more complex are associations of different natural regions such as 
form the British Isles or Iberia or Scandinavia. 
There are therefore various orders of natural region, which we may roughly 
compare with the species, genera, orders, &c., of the biologist. For these we 
may have no definite names. Tentatively we may speak of species, genera, 
orders, classes of natural regions, even though this suggests biological analogies 
which may mislead the beginner. From this point of view valley, plain, and 
plateau are chorographical species each with many varieties. These them- 
selves may be grouped into different genera of mountainous-, platean-, and 
plain-lands, and these again into different orders of country, compounded of 
different combinations of these, which finally grouped together compose the 
continents. 
This morphological or topographical classification is not enough. Climate 
must be taken into account in the larger divisions. The need for this is most 
easily recognised in the vast plains, where vegetation affords an index of climatic 
and edaphic influence. The botanist’s classification into plant societies, 
associations and formations suggests new groupings, which have to be considered 
in making natural regions. 
Beginning with the continents we might recognise major natural regions, each 
with its own climatic rhythm, and this acting on different genera of land forms. 
These topographical genera enable us to determine the geographical genera, 
which may themselves be sub-divided into different geographical species, each 
of which may have a number of varieties. 
I venture to suggest as a convenient nomenclature for the geographical 
* One other class—the cone, usually volcanic—may be mentioned. Only 
rainy régions are considered for the moment. 
