28 THE OPEN BOOK OF NATURE 
The stratified rocks are called “ secondary ”’ because 
their material has been derived originally from 
primary or igneous rocks, and they are called “ strati- 
fied’? (Latin, stratum=strewn out) because they 
occur in layers and beds. The accompanying 
diagram (Fig. 2) will enable you to form an idea of 
the appearance of stratified rocks. 
Stratified rocks have been laid down as Sedi- 
mentary Deposits by the agencies already written 
about at some length at the beginning of this 
——s- = = ie a 4 
| ae peeial Bg \ Se SO Re Se Sr ee See trea 
= ” ame ee —_—_— B = 4 
per 4 
Top and bottom strata sandstones, the two dark layers=shales, 
and the centre bed = limestone. 
chapter. These deposits are found as sand, such 
as is seen at the seashore, or in sand-dunes, or in 
the great deserts of the world, and also as gravels, 
sandstones, grits, conglomerates, breccias, muds, 
clays, claystones, slates, marls, and loams. Let me 
briefly describe these different deposits : 
Sand is commonly formed of worn grains of quartz 
derived in the first instance from the wear and tear 
of primary rocks. Examine any sands you can get 
samples of under your magnifying-glass. Some 
