Although the world offers many different aspects of closed vegetation, they may all in a broad sense be reduced to two general types--namely, grasslands and woodlands, the former the result of a lighter, the latter of a heavier, rainfall: grasses and their associates requiring for their life-processes a much less amount of water than a tree vegetation. The British Isles lie within a broad belt that sweeps east and west across Europe, characterized by a prevalence of south-west winds laden with moisture, and yielding a tolerably heavy rainfall distributed throughout the year. South of this belt--south of the Alps, roughly--the rainfall occurs chiefly in winter, and dry summers produce the well-known “Mediterranean climate” with which is associated the scrubby small-leaved vegetation, capable of withstanding heat and drought, which is characteristic of Spain, Italy, Greece, and Northern Africa. Northward, the forest-belt extends into Scandinavia, dwindling into a tundra vegetation of lowly shrubs and herbs as we approach high latitudes with a sub-arctic climate. Forest, then, is the original and natural type of vegetation of the British Islands, and without doubt the greater part of the country was occupied by woodland within the human period. But forest country is not well suited to human habitation or colonization. The early arts of peace--pastoral and agricultural--called for open ground. To operations of war, also, forests are unfavourable. So it came about that by the use of fire and axe the forests passed away before the march of man, until now we can study only fragments of the original all-prevailing woodland. But it is important to note that certain portions of the British Isles were never, in recent ages, under woodland, and that these mostly preserve still much of their ancient facies. Thus, increase of exposure--a lower temperature and higher wind-velocity--appointed a limit on the hills beyond which trees could not and cannot grow. Wind was and is also responsible for a dwindling of tree growth along the exposed western coastlines. Again, the shallow, porous soil of the chalk downs, very dry in summer, probably never supported woodland, but has pastured sheep since the earliest shepherds fought wolves in Sussex. The scanty soil of Farleton Fell probably never harboured plants larger than the herbs and low shrubs which it now supports; and no doubt the salt-marshes looked the same five thousand years ago as they do to-day, though their positions have changed with each slight alteration in the relative level of land and sea.