30 THE OPEN BOOK OF NATURE 
logy you will know something of the Millstone 
Grit. 
Conglomerate is a rock composed of gravel and 
shingle cemented together by a paste, which may be 
a kind of clay, or a natural mortar of sand and lime. 
Conglomerate is sometimes called “‘ pudding ”’ stone, 
Breccias (pronounced. bretchia) are rocks formed of 
angular fragments such as are found in heaps of 
material lying at cliff bottoms. The angular frag- 
ments in breccias cannot have been subjected to 
much movement, or they would have been rounded 
like pebbles that are water-worn. So when you 
find breccias you will know that the materials of 
which they have been formed had their original 
position near to or at the place where the rocks are 
now situated. 
— Clay, as you know quite well, is an exceedingly 
useful sedimentary deposit. Where would our 
bricks, tiles, and drainpipes be without clay ? And 
what should we do for crockery ? Clay is usually 
deposited as mud on the floors of seas and lakes. 
It is composed of exceedingly fine particles of various 
materials, such as felspar and quartz. These 
particles, the fine dust formed by wear and tear of 
rocks, are carried in suspension in water to great 
distances. A running stream carries heavy frag- 
ments short distances ; it washes sand to greater 
distances, and the finest particles of matter, which 
slowly drop to the bottom of seas and Jakes as mud, 
and become clay, are carried farthest of all. When 
you moisten clay it becomes soft, and it can be 
moulded to any shape. Mix clay with water, and 
you have mud. Clay under heavy pressure becomes 
