Commagene, where not rocky, and the district lying along the southward drains from its divide (anc. Cyrrhestica), is in better case, enjoying perennial streams which can be utilized, and the fringe of the Tauric rainfall.
The White Horse Hills and the Chilterns strike right across the Thames basin, but almost their entire drainage from either flank lies within it, and similarly a great part of the low-lying Weald, though marked off from the rest of the basin by the North Downs, drains into it through these hills.
The greater part drains to the Mediterranean, from which the land rises gradually to the summit of the Tih plateau.
The great river thus constituted drains an area of about 1,250,000 sq.