6 EVOLUTION MADE PLAIN 
ape. They are as distinct species as is man 
himself. 
GEOLOGICAL EVIDENCES OF PROGRESSIVE 
DEVELOPMENT 
All life on this globe is divided into two 
great classes, vegetable and animal. All ani¬ 
mals belong to one or the other of two grand 
divisions: invertebrates (those without back¬ 
bones) and veterbrates (the backboned). The 
latter class, comprising more than 30,000 known 
species, is subdivided into five great groups: 
fishes, frogs, reptiles, birds and mammals. At 
the top of the highest group, mammals (those 
which bring forth their young alive), is man. 
Birds and mammals were evolved from the rep¬ 
tiles—both offshoots of the same stock—and 
are contemporaneous in development and de¬ 
scent. 
The various classes and groups of animals, 
both in the order of development from the 
simple to the complex and in the time of their 
arrival, are in the order named: first the small, 
one-celled animals (many species of which are 
found today) then more complex organisms of 
the invertebrate division, later the fishes, am¬ 
phibians, reptiles, and mammals, including 
man. 
The story told by the geologist is in perfect 
agreement with those laws of development 
which we call evolution. The lowest, simplest 
forms of life are the oldest as is shown by 
their fossil remains (bones, shells, etc.) found 
in stratified or water-laid rock. These fossils 
were deposited in sediment as it formed in sea 
