Before the modern industrial system the economic centres of production were the wheat lands, and these were the open land of which Winchester was the centre, the Dorchester centre, Somerset, certain separate centres in the Midlands (separated by great woods which have disappeared and their exact site not certain), the Cheshire Plain, the Lancashire Plain, the great Yorkshire Plain, and last, and most important of all, East Anglia--the central Eastern plain (Essex in particular) was the granary of the early time in England. Tracks connected all these places: they also connected the centres of population with the ports. Every one of the tracks makes ultimately from port to port. You have a connection through London (earlier perhaps, as we have seen, through Lambeth) between the port of Kent and the north-western ports (of which Chester is the great original example and Liverpool the modern); between the north-eastern ports of the Humber and the Tyne, and the south-western ports at Southampton Water and Poole (which was of great early importance, and whence we shall find a Roman road starting). Further west the mouth of the Exe was a more important approach to Britain in the past than it is now. You have also the estuary of the Severn, ill provided with natural harbours but forming in its upper reaches a harbour of its own, with the peculiar advantage of the lower Avon, with a secure pool at Bristol approached by the curious and exceptional gorge at Clifton. Lastly, you have the great port formed by the crossing place at London, made, as we have seen, by the tendency of early travel, right up to the appearance of railways, to penetrate a country as far as possible by its waterways and to carry cargoes well inland, because water carriage was so much cheaper than land transport. The third factor--that of river crossing--also has its effect, though a lesser one, upon the trace of the old British ways. If, for instance, you carry along any one of the tracks which follow the chalk you will see how carefully the water crossings were picked. It is the characteristic of chalk that the rivers lie transverse to it, cutting gorges through the hills, and each of these crossing places was chosen where hard land approached from either side. The chalk (and the sand associated with it) provides at certain points in the valleys twin spurs approaching the water on either side; hence you have the track along the north downs crossing the Wey at St. Catherine’s Chapel (and alternatively by Guildford); and, again, the Mole at Pixham, near Dorking, and the Medway at Snodland (with an alternative at Rochester). The southern track along the Hampshire and Sussex Downs takes the Arun at a similar advantage and opportunity at Houghton, and alternatively at Arundel. It takes the Adur at Bramber, the Ouse at Lewes.