HOW SCENERY IS MADE 
91 
world’s history, for all nummulitic limestones belong to quite a 
late geological epoch. On the other hand, the Malv'ern Hills are 
some of the oldest in the world. 
All the limestones mentioned thus far were of marine origin, 
but in the Isles of Portland and Purbeck, what is known as 
Purbeck marble, often used for small pillars in churches of the 
south of England, is of fresh-water origin, as may be readily 
perceived by the character of the numerous shells which abound 
in it. 
Limestones, if soft, are easily worn down by running water ; 
so that deep ravines and river valleys often characterise a lime- 
stone table-land, such as the Stroud Valley in Gloucestershire, 
through which the Great Western Railway passes, and the 
country about Matlock and Buxton in Derbyshire. 
The kopjes of South x\frica are the results of denudation, the 
rivers and spruits having cut away the intervening spaces. 
Besides being mechanically worn down by it, water will take 
up a great deal of lime in solution ; and, as the rock is always 
full of cracks, surface-water penetrates down and dissolves the 
limestone, continuall}' widening the cracks and loosening blocks. 
As this goes on for countless ages, the water in time forms a 
tunnel for itself, and consequently whole rivers may flow for 
miles underground, issuing out at some lower level. Thus the 
Peak of Derbyshire is an elevated flat-topped plateau under- 
mined in this way by the river, which finally issues at the 
Peak Cavern. 
Enormous caves formed in this way occur in some limestone 
countries, as in Kentucky. Derbyshire is celebrated for them ; 
and as the water, trickling down with the lime dissolved in it, 
evaporates, it deposits the carbonate of lime in the form of 
“stalactites,” suspended from . the roof, just as water forms 
icicles by freezing, while the “ stalagmite ” accumulates on the 
floor. 
One feature of a limestone country consists in long winding 
and narrow valleys, with precipitous limestone walls on either 
side, such occur at Cheddar ; and it is believed by some 
geologists that these were originally formed by subterranean 
rivers, the roof having gradually fallen in, so that they now are 
open to the sky. Others attribute them to ordinary erosion by 
a river, now diverted. 
With regard to the uses of limestone, the most common is 
as building stone, as at Bath and in Derbyshire. When hard 
enough to be polished as marble, it is of course used for all 
kinds of decorative work. 
Burnt limestone and chalk supply quicklime, by driving off 
the carbonic acid, which in combination with lime forms lime- 
stone, this being really carbonate of lime. 
If the lime be in combination with sulphuric acid, it is called 
gypsum or sulphate of lime. This sometimes forms consider- 
able masses of rock imbedded in others, but does not affect the 
scenery. 
