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 northern slope of this great plateau is drained by the AraguayaTocantins, Xingu, Tapajos and Guapore-Mamore-Madeira, which flow northward, and, except the first, empty into the Amazon; the southern slope drains southward through a multitude of streams flowing into the Parana and Paraguay.
25), is to be seen at the south-west corner of the city; it is an enormous excavation in the rock with drains in its sides, at the bottom of which there is now a flourishing orange garden.
It grows in marshes, ditches, pools and drains in meadows, and sometimes obstructs the flow of water with its dense matted roots.