Escarpments are the prominent outcrops of flat or gently inclined strata, exposed by denudation. They may be regarded as the steep edges of hills in retreat. The British islands abound in admirable examples of all ages from early Palæozoic rocks down to Tertiary deposits, and of every stage of development, from an almost unbroken line of cliff to scattered groups of islet-like fragments. The retreat of our escarpments can be well studied along the edge of the Jurassic belt from Dorsetshire to the headlands of Yorkshire, likewise in the course of the edge of the Chalk across the island. Not less suggestive are some of the escarpments of more ancient rocks, such as those of the older Palæozoic limestones, the Old Red Sandstone of Wales, the Carboniferous Limestone and Millstone Grit of Yorkshire, and the Coal Measures of the Irish plain. Our volcanic escarpments are likewise full of interest, as displayed in those of the Lower Old Red Sandstone along both sides of the Tay, in those of the Carboniferous system in Stirlingshire, Ayrshire, Bute, and Roxburghshire, and in those of the Tertiary series in Antrim and the Inner Hebrides. THE PLAINS. The Plains of Britain, like those elsewhere, must be regarded as local base-levels of denudation, that is, areas where, on the whole, denudation has ceased, or at least has become much less than deposit. Probably in all cases the areas they occupy have been levelled by denudation. Usually a greater or less depth of detrital material has been spread over them, and it is the more or less level surface of these superficial accumulations that generally forms the plain. But in some instances, such as the flats of the Weald Clay and the Chalk of Salisbury Plain, there is hardly any such cover of detritus, the denuded surface of underlying rock forming the actual floor on which the vegetable soil rests.