Geology, Relief & Drainage.

D. and N. occupy a low ridge between two Tame tributaries, which declines gently from 400 feet at Gosta Green to 352 feet at High Park Corner and 290 feet at the Tame/Rea confluence. The silt-floored valleys are about 50 feet below the ridge-top. According to the O.S. Solid Geology Map, the bedrock is Keuper Sandstone, a porous red material useful for building but prone to wear and crumble (see the railside wall on Melvina Road, built of rock dug out of the cutting nearby). East of a fault which runs from Saltley Viaduct to Curzon Street Station the bedrock is shown as Keuper Marl, an impervious red clay which makes excellent bricks and tiles.

It should be noted that on the 1758 Map brick-kilns appear in Ashted and north of N. Place, where the Survey shows sandstone. However these Triassic sediments of whatever composition have been of less importance as factors in settlement and communication than are the glacial drift layers of sand and gravel, said to be 55 feet thick at greatest, which the Survey found wholly covering the area. The drift is porous and only moderately fertile, provides springs and wells, dry dwelling sites, and fairly firm going. Natural vegetation upon it would vary from oak woodland to open heath, according to the degree of stoniness and porosity. The boggy floodplains on three sides would be fringed with willows : Saltley on Rea's other bank means 'clearing among the willows', while Gosta is a corruption of Gorsty which indicates the prevalence of furze-bushes, natural to drift.

The very gentle gradient of the silted valleys caused the streams to meander and divide into a number of sluggish channels : but after heavy rain the whole width of the flood-plains could be quickly inundated. The Rea, fed by many tributaries from the Lickey Hills, would briefly become a noble river a furlong wide.