When the use of artificial material for the surface of the track became common this question of quality of soil was somewhat modified, but its essential was retained; for what made bad going (in the North, and particularly in Britain) being heavy soil, that same kind of land, which interfered with foot or pack-horse travel, swallowed up material. It was a less grave inconvenience than in the times before artificial material was used, but it was still an inconvenience expressed in the shape of expense; and nearly all the original trackways continued to take account of this factor long after the use of artificial material had been introduced. The earliest of all, of course, follow the dry ridges, and in particular the chalk. One may say, with slight exaggeration, that the chalk was the essential factor in the building up of British communications before the Roman civilization came. If you take a geological map of England you may see the great chalk ridges radiating in a sort of whorl from a centre in Salisbury Plain, and providing dry going to the Channel, the Straits of Dover, and across the Thames valley at Streatley right on to Norfolk. Another example of a road taking advantage of dryness of surface is the straight line leading to Lincoln northwards, everywhere following that peculiar isolated ridge, with low-lying ground upon the left and marsh upon the right. Another very striking one is the Hog’s Back, where from one low-lying point to another (Guildford to Farnham) the primitive track deliberately rises and follows the summit of a high hill between rather than the wetter ground upon the slopes, though here there is an alternative upon the southern, or sunny, slope where the trackway leads through to St. Catherine’s Chapel. This is a modern example of the way in which a primitive track imposes itself upon posterity. To this day your motorist climbs up that roof of a house out of Guildford and goes down the steep on to Farnham because countless generations ago his ancestor could only be certain upon that height of dry ground. In the South (which does not concern this essay) the great obstacle in the way of soil is not marsh, but sand. That is something of which we have here no experience, but the tracks of nearly all Western Islam are dependent upon it. Drift sand is not so impassable as marsh by any means, but it is terrible going. North and South of Atlas the knowledge of how this kind of soil may be avoided is half the business of establishing a primitive road.