50 THE OPEN BOOK OF NATURE 
become extinct. In Palszozoic times there were 
kinds of fish, sea-lilies, starfish, sea-urchins, and 
corals, which did not live beyond the Era. There are 
no traces of birds or mammals in these early for- 
mations. The Graptolites became extinct at an 
early Period. 
Tuer Mesozoic ERA. 
3 
The name “ Triassic ’’ was given to the rocks it 
represents on account of their threefold develop- 
ment in Germany. The Jura Mountains, where 
‘‘ Jurassic’ rocks are well in evidence, give their 
name to the strata of this Period. The term “ Cre- | 
taceous ” (Latin, creta=chalk) is given to the rocks’ 
of the Period in which chalk is very conspicuous. 
The Mesozoic Era was the age of Great Reptiles, 
some of which I shall describe. But, of course, a 
great many forms of life existed in addition to the 
Reptiles. Some new forms of sea-lilies, fishes, and 
sea-urchins, as well as ammonites, appeared in those 
times, and some birds were in existence. 
THE CAINOZOIC ERA. 
I do not think I will tabulate the strata of this 
Era. As their name implies, they enclose fossils of 
recent, although not always existing, forms of life. 
The Paleozoic rocks are sometimes called “ Pri- 
mary,” the Mesozoic ‘‘ Secondary,”’ and the Caino- 
zoic “‘ Tertiary,’ the more recent rocks of the Era 
being often named ‘‘ Quaternary.” The Periods of 
the Cainozoic Era are the THocene (eos=dawn, 
