66 NATURE NOTES 
easily cut out, as the cementing process is in places very 
deficient. 
In Warwickshire and Herefordshire there is much sandstone, 
coloured red ; whence these two have been called by geologists 
the “ new red ” and “ old red ” sandstones respectively. Houses 
and St. Mary’s Church, in Warwick, have been built of it. 
Sandstone countries have no very special features. Being, 
as a rule, comparatively easily denuded by water, we get flat or 
undulating country, as in Warwickshire and Sussex and Here- 
fordshire, where there are deep ravines, such as that of the river 
Wye ; so that the scenery may be in parts very fine. 
If the sand contain small pebbles it becomes gritstone, of 
which there is much in Yorkshire. This is used for millstones, 
and therefore it is called “ millstone grit.” 
A curious quartz-pebble bed, of which only solidified frag- 
ments are now found about St. Albans, consists of small rounded 
flint stones embedded in a fine silicious “ matrix.” It has been 
called “ plum-pudding stone.” In other words, the sand was 
ground down to a powder like meal. A similar bed, only per- 
fectly incoherent and nowhere solidified, occurs in a quarry near 
Chislehurst ; while a huge block of pudding-stone, probably 
transported there by an iceberg, stands in the village of White 
Notley, Essex. 
If sandstone and gritstone undergo great compression and 
heat, the grain and pebbles become semi-fused and consolidated, 
constituting quartz-rock. Bands of this, in which the pebbles 
are still sometimes distinguishable, occur among the slate-rocks 
of Wales. In some of the coal-mines they sink shafts through 
thick beds of sandstone, which originally overflowed the forests 
and swamp-vegetation, now turned into coal and so buried it. 
Sometimes trees decayed away, leaving great pipes in the sand- 
stone beds ; subsequently becoming filled up and hardened, 
they took the form of the original trunks of the trees. A large 
specimen may be seen standing in the grass at the east end of 
the Natural History Museum, South Kensington. 
The chief mineral in sand is quartz, and the most important 
use of sand is for making glass, since quartz will readily fuse with 
potash or soda. The old story says that some sailors, using the 
herb salt-wort for kindling a fire on a beach, found some “ glass ” 
left behind. Such was the original discovery of the means of 
making glass. Quartz in various forms is probably more or less 
familiar to the reader, such as quartz crystals or “ rock crystal,” 
from which the so-called “ pebble ” eye-glasses are made. This 
has no advantage over pure glass, except that it will not chip. 
Of gems there are amethyst, coloured violet with manganese 
oxide ; cairn-gorm, yellow or brown, coloured by iron : opal, 
cornelian, chalcedony, agate and onyx are “ hydrated ” banded 
forms, while cat’s-eye owes its peculiar flashing appearance to 
the presence of filaments of asbestos. 
George Henslow. 
