52 THE OPEN BOOK OF NATURE 
kainos =recent), in which existing species of shells 
began to appear; the Oligocene (oligos=few, and 
kainos), when there were few recent shells; the 
Miocene (meion= less), when there were really more 
recent forms, but they totalled less than the older 
species ; the Pliocene (plios=more), when shells of 
existing species came to be more in proportion to the 
old shells ; and the Pleistocene (pletstos =most), the 
shells of this Period being all represented by still 
living species. The Cainozoic Era is known as the 
“Age of Mammals,” for horses, elephants, mam- 
moths, and a host of other mammals came into being 
in Cainozoic times, and their fossil remains are 
found in the rocks of the Era. 
I have just finished presenting you with a mass 
of dry details, which may not prove so fascinating 
as a fairy-tale, but they are details which the would- 
be geologist must bear in mind. For fear of over- 
burdening you I have omitted to set down a good 
deal of information ; indeed, I have given you a 
very bare outline. For the fullest particulars you 
must refer to books devoted entirely to the science. 
What I want to make you understand is, that you 
must study your fossils in a systematic and scientific 
way. It is not sufficient for you to collect a few 
fossils and give them names ; you must be able to 
tell the Eras and Periods to which they belong ; and 
the time will come, I trust, when you will have such 
a thorough grasp of your subject that you will be 
able to form clear mental images of the living 
creatures or plants represented by fossils, and also 
of the circumstances in which they flourished. 
From the tabulated figures you will see that the 
