This capping of clay permits the growth of forest on the hills, as do the alluvial deposits in the valleys; so that in its well-wooded character the scenery of the greater part of the county is altogether different from that characterising the bare North and South Downs and the Chiltern Hills. Where the chalk comes near the surface there is a marked tendency to the growth of beech-trees, splendid examples of which may be seen in Beechwood Park. Elsewhere in the chalk districts the elm is the commonest timber-tree; although it should be said that this species of tree was originally introduced into England from abroad. Reference has already been made to the numerous open commons dotted over the chalk area of Hertfordshire. These appear to have been left as open spaces at the time the country was enclosed, owing to the sterility of their soil, which is unsuited for growing good crops of either corn or grass. Many of these commons, as in the neighbourhood of Harpenden, were enclosed some time previous to the battle of Waterloo, when corn in this country was so dear, and every available piece of land capable of growing wheat consequently of great value. It may be presumed that the commons with the best soil were selected for enclosure; but most of such enclosed commons produce inferior crops, partly, it may be, owing to the plan on which they are cultivated. Till twenty years ago or thereabouts all such commons in the writer’s own neighbourhood were divided into a number of parallel strips, separated by grass “baulks”; these strips representing the respective shares of the copyholders of the district, who had the right of grazing on the original common. The absence of hedges rendered it necessary that the same kind of crop should be grown each year on every plot. This made it not worth the while of the occupiers to spend money on high cultivation. Of late years many of these enclosed commons have either been built over, or come under a single ownership, thereby obliterating one more interesting page in the history of the county. To the south of the Elstree range of chalk hills the scenery suddenly changes, and on emerging into Middlesex from the tunnel through these hills on the Midland Railway we enter an extensive grassy plain, characterised by its abundance of oak trees, the scarcity of elms, and the total absence of ash. Parts of this plain, which is continued through Middlesex to London, form the great grass-growing and hay-producing district of Eastern Hertfordshire.