46 THE OPEN BOOK OF NATURE 
you find chalk with its characteristic fossils in a 
high and dry land surface, you know it was at one 
time a sea-bed. If you find remains of trees firmly 
rooted in a sea-bed, you know that it was once a 
land surface. The reindeer flourishes in a cold 
climate, and it is fair to presume that a cold climate 
once obtained in regions where its fossil remains are 
found. If you discover deposits containing bones 
of elephants and lions, and leaves of tree-ferns or 
palms, you conclude that the climate was tropical 
when the deposits were formed. Fossils, moreover, 
help you to understand the great procession of life, 
how certain creatures lived and flourished in certain 
periods, and by-and-by became extinct, to be fol- 
lowed by other creatures superior to them in many 
ways. Certain fossils are associated with particular 
formations, and we are able to know a formation by 
the fossils it contains. 
The stratified rocks have been deposited through 
an incalculable period of time. The oldest of them 
are so old that it were foolish to even guess their 
age in years. But we know something of the order 
in which they were laid down, and the fossil contents 
of rocks enable us to decide which rocks are very 
old, which are less old, and which are of com- 
paratively recent date. I am now going to give 
you the order of the stratified rocks from the earliest 
to the most recent. Geological time is divided in 
Eras, which are four in number : 
1, Kozorc (Greek, eos =dawn, zoe = life). 
2. Patmozorc (Greek, palaios =ancient, and zoe). 
3. Musozorc (Greek, mesos = middle, and zoe). * 
4, Catnozorc (Greek, kainos =recent, and zoe). — 
