Below the balustrade of a terrace, a wall fountain finds a suitable place. A fountain of this kind, with a semi-circular dripping pool below, approached from the terrace by twin stairways, is a device that is very popular in gardens of certain types. A simpler design would substitute a grassy bank or dry retaining wall as a division between the two levels. Of these alternatives, the grass banks are most troublesome to keep in order owing to the difficulty of trimming, and walls are more common in consequence. A nearly vertical wall, with a stout balustrade at the top, is most practical where the difference in level is very great between the garden and terrace.
If grass banks are made, they should rise one foot for every two of horizontal breadth, any steeper slope being too ready to dry out during the summer.
Slight differences of level are best divided by dry retaining walls, planted with colourful rock plants—Aubrietias, Arabis, Pinks, Stone-crops, and Ferns. At the base of the dry wall a narrow border is better than if a grass lawn runs right to the rocks, since it is not possible to cut grass close to the wall with a mower.