The geological structure, the relief, the climate, and the location in respect to the continent all combine to create a strong contrast from northwest to southeast. The differences are well exemplified along a line extending only two hundred miles from the Island of Anglesey in northwestern Wales to London and its suburbs in Kent. Of course the transitions from one extreme to the other are often irregular and some steps may be missing. Nevertheless, the transition is on the whole so clear that we may sum it up in the form of a table showing the types of changes from northwestern Wales to Metropolitan London:
1. From the oldest rocks to the youngest.
2. From moderately high altitude and rugged relief to low altitude and gentle relief.
3. From thin, poor, acid soils that can be worked with difficulty to deep, easily worked, and fairly fertile soils.
4. From almost uninhabited tracts hundreds of square miles in extent to one of the world's two main conurbations, or urban aggregations.
5. From a very moist climate, with constant rain and cloud and a small range of temperature, to a climate with only half as much rain, more sunshine, and a distinctly greater range of temperature.
6. From an almost purely natural landscape of grass, heather, moors, bogs, and treeless windy wastes to an almost purely manmade landscape of fields, hedges, villages, cities, factories, roads, and railways replacing a natural landscape of deciduous forests with large broad-leaved trees like the oak, elm, and ash.
7. From pastoral agriculture based on sheep and natural pastures to horticulture where orchards and market gardens predominate.
8. From old, long established, conservative racial stocks to young stocks representing comparatively recent migrations.
9. From almost purely agricultural communities with practically no cities or even villages to a commercial, industrial, and political community embracing a quarter of all the people in the country.
The outside world thinks of Great Britain as a very unified country but in reality it is highly varied. In the United States the contrast between New York and the southern communities of cottonraising colored people who live in board shanties with shutters instead of glass windows is perhaps greater than between London and the shepherds of Wales in their gray stone huts, but one has to travel four times as far to see it. Moreover, there is by no means so great a change in density of population and in scenery. On the continent of Europe, too, it is not easy to find such great and systematic contrasts within the limits of a single country unless one travels long distances as in Russia, or from a high altitude to a low as in going from the Alps to the Po Valley. The reason for all this is the marginal location of Great Britain to which reference has already been made. The country lies close to the border of the favorable portion of the world. Hence even a small increase in altitude, such as occurs in Wales and Scotland, lowers the temperature and increases the rainfall so much as to alter profoundly the conditions of human existence.