THE CAMBRIAN PERIOD. 
37 
like our sponges. Almost everywhere in these rocks 
are found coral fossils. I noticed three leading 
kinds, named, from their shape, cup, honeycomb, and 
chain corals. As corals can not live in cold water, 
so far as we know, and these coral fossils are found 
even in w^hat are now arctic regions, the seas must 
have been more or less tropical all over the world. 
Other fossil remains of animals look like beaded pic¬ 
ture-molding ; they are known 
by the name of graptolites. I 
have often found in these rocks 
animals that look like lily- 
buds, called crinoids. In their 
manner of life they did not 
differ much from our sea- 
urchins and starfishes that also 
existed in that age, as we may 
see from the fossils discovered. 
The stone lilies, however, are 
fixed by a stem to some object 
Figs. 16 and 17.—Graptolites. 
in the sea, while the sea-urchins and starfishes can 
move about. 
Thus we see that life made a beginning in all its 
types below the vertebrates. There were protozoans, 
echinoderms, coelenterates, mollusks, and crustaceans. 
4 
