ESCARPMENTS AND PLAINS 151 



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 Palaeozoic 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 Dor- 

 setshire 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 Palaeozoic 

 limestones, the Old Red Sandstone of Wales, the Car- 

 boniferous Limestone and Millstone Grit of Yorkshire, 

 and the Coal Measures of the Irish plain. Our vol- 

 canic 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 Carboni- 

 ferous 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 



