CHAPTER IV
THE OBSTACLE OF VEGETATION
The Special Expenditure due to Forest: Roads which Skirt Woodlands: Roads which have been Deflected by Forest: Proximity of Material as a Final Main Cause Modifying the Trajectory of a Road: Cost of Transporting Material and its Effects in Ancient and Modern Times.
The obstacle of vegetation, which is our next cause modifying the trajectory of a road, is two-fold. There is the obstacle presented by forests or permanent vegetation (which includes in some climates very high grasses) and the obstacle presented by intermittent growths. We are not, in this country and in modern times, well acquainted with the obstacle of vegetation to a road and with the modification of trajectory which it imposes. We have no large forests left: we have, in common with all Northern Europe, no exuberance of growth. The dense population and very high road mileage of modern England have put this factor in the development of communication out of sight, and it is so unrecognized that the mention of it here may seem superfluous. But it is still a grave element in the calculation of a road even in the European world, and a graver one in the new countries. And it has had its part in framing our own system in its earlier stages. In damp tropical countries it is all important, and even in temperate climates where large forests exist it has its place.
(a) Forest. Two special expenditures attach to this obstacle: First the effort of clearing a way, second the effort of maintenance, and particularly through the effect of wood upon surface. The effort of clearing, always an expense, made the forest in very early times an insuperable obstacle to any great or considerable road. The forest had tracks, but the main road was compelled to skirt the denser woodland, or at the least to take a tortuous trajectory for the advantage of natural clearings. With the development of civilization that difficulty disappeared, and it disappeared early, although I can call to mind no broad primitive track through any dense woodland. The Roman roads hewed their way through forests where it was necessary, and found in the value of the timber felled an economic compensation for the effort made. But even with them, and even with modern roads, it remains true that the forest governs and modifies road construction. There is case after case where a Roman road, and even a modern road, will skirt a forest rather than be at the effort of overcoming the obstacle: for instance, the case of the forest of Mormal in Northern France. Here the main Roman road from the centre of Northern Gaul to the crossings of the Rhine cuts along the edge of the great wood like a knife, with no growth on its western side. Further, cause and effect reacting on one another, the lack of roads preventing clearing, and the lack of clearing keeping down habitation and so ways, there is no great forest possessing a system of roads anywhere in Europe. All considerable stretches of woodland, where agriculture or other economic effort has not cleared them, have a minimum of roadway.
In our northern climate, the larger stuff once felled, upkeep is not a grave economic matter. The use of artificial material, which comes in at the very first stages of road-making, renders the problem here even less important. But in other climates, and particularly in the tropics, it becomes the dominating factor. There are whole districts—as, for instance, on the Amazon basin, or, again, in Central and West Africa—where the problem of communication consists not in the cutting of the original track, expensive as that is, but in its maintenance; and in the greater part of those districts even modern civilization, with its immense material advantages, and with its strong economic inducement to the transport of tropical material, has been unable or unwilling to make and maintain forest roads, at any rate for ordinary wheeled traffic.
With the railways it is otherwise. The economic effort required for the construction of the track is such that the added expense of clearing the forest is a much smaller fraction of the whole, and the type of bed which has to be established for the track partially solves (but only partially) the question of upkeep. Even the railway can be overcome by the vigour of tropical vegetation, but it has a better economic basis in the densely wooded country than has the Road.
One of the most curious facts in the history of roads due to the obstacle of wood is the deflection of the Roman Road through this cause after the decline of civilization. One can find many instances of this even in England, light as is the afforesting of this country, and small as are the districts affected. Thus the Great North Road making for Stamford is a broad, unmistakable way raised high above the neighbouring country, and looking like some great double rampart, from the crossing of the Welland for miles to the north and west. It approaches a small patch of wood on a hill and disappears. It remains lost for a mile after its destruction by the wood, and is not found again in anything like its earlier sharpness of outline till Stamford is reached. That is because the upkeep through the wood became too difficult in the Dark Ages, and men turned the obstacle by developing a new road round it. Another very clear example is to be found on the Stane Street north of Eartham, where the great Nore Wood through which the Roman road was driven usurped it in later times, overgrew it, and deflected the modern road round by Duncton Hill. We have here probably not so much a case of keeping down the new growth as of the wetness of the track when artificial material ceased to be used, and of the difficult going thus made between the trees. The occasional fall of trees across the road left unremoved, and the danger in such times from any close cover must not be neglected. But, whatever the cause, woodland perpetually deflects a Roman road after the breakdown of the old civilization. It deflects it almost as often as does the marsh of a river valley.
(b) The obstacle to the making of a road due to intermittent vegetation is one which plays no part in our system, and is unknown to our climatic conditions. Nor is it of any great effect save in a few special highly characterized regions of the world. The track, once established, can commonly keep down even the riot of spring vegetation in open land. Such exceptions as there are, due to the exceptional development of grasses, affect no part of the world where communications need high development. The factor exists, but needs no more than a mention.
The last main cause modifying the trajectory of a road is the relative proximity of material for its construction, using the word “proximity” in the wider sense to include all economic effort: what to-day we call the “cheapness” of the material.
Even in the very simplest and most primitive form of roadwork material enters. There is always the necessity of hardening some bit of soft ground or of smoothing some bit of unevenness, and from the beginning of travel you have had the transportation of material to the established road for the improvement of its surface, for the bridging of its water obstacles or flooring of fords, for the making of its causeways over marshes.
In what may be called the middle period of road construction—that is, in periods of high civilisation, but civilisation not provided with modern instruments—the immediate neighbourhood of material introduced a considerable modifying factor into the trajectory of a road. This was often masked, from the fact that the same soil which provided good going and therefore developed early tracks usually also provided, in the nature of things, good material for hardening the surface, for the building of causeways, and even for the throwing of bridges. It was also masked by the fact that the bridge, if it were to be built of wood, could get its material from a considerable distance, as the river was its avenue of supply. But though transport of material has gone through a revolution in the last hundred years, and material for road-making is now brought half across the world (e.g. Colonial wood pavement), yet the way neighbourhood of material tells can still be seen everywhere upon the road map of Europe. Thus the absence of main roads in the Fens for centuries was not only due to the necessity of continual artificial work, embankments, and bridges (this would not have deterred the Roman road-makers nor the great effort of the early Middle Ages from attempting a full network of roads). It was rather due to the absence of hard material. And you have the same phenomenon in the Landes of South-western France, where to this day only one great road serves an immense district whose loose and sandy soil fails to provide a cheap and sufficient material. The traveller in Holland notices the same thing: here are roads ultimately depending upon brick paving and narrow, where, had there been abundant material available, they would have been broad, for they had to carry a great deal of traffic. The alternative water traffic by their side was largely developed by the difficulty of making the road.
The Romans fought this difficulty with singular tenacity. They made all their great public constructions to last, as it were, for ever; and they made their roads with such a strong political and military object that they would not be deterred save, as in the Fenlands, by the gravest difficulties in the obtaining of material. Thus in such of their roads as start anywhere near a sea-beach of shingle you will find them using that material up-country for miles, and they will make deep foundations for roads that have to cross clay, using, sometimes, hard stone brought over a couple of hundreds of miles of sea and some thirty of land travel. It is a difficulty which has not disappeared to-day. It has been very greatly lessened by modern means of transport, but it still appears. We see it throughout modern Europe: for instance, in the varying surfaces of the different soils. The ideal surface of broken granite is not nearly universal even in England, as one would think modern transport would have made it long ago, over such a small area with such masses of granite close at hand and accessible by sea. The relative cost of transport still makes diversity of surface the rule. One can make a sort of economic barometer based on the use of granite. It extends farther and farther from the sources of supply as public wealth expands, and recedes towards them as public wealth diminishes. We have a first-class example of this in the case of flint versus granite. Flint has its advantages over all other material in hardening a roadway. It is at once hard and easily broken: it is superficial, and therefore cheap: it is abundant in supply in the districts where it is used. On the other hand, it has the gravest possible disadvantage for modern motor traffic, which is its effect upon the tyres indispensable to that traffic. One could draw a graph, I think, to cover the last ten years showing the fluctuations of this material and granite upon the main roads of Southern England, and the curve would follow the opportunities of supply and of public expenditure as affected by the Great War.