410 ELEMENTARY GEOLOGY 
In one important respect the life of the Ordovician 
certainly differs from that of the Cambrian. Records 
of land hfe, both of plants and animals, are found 
FiG. 235. 
A group of Ordovician fossils. 1, 3, 4, 6, and 10, 
brachiopods; 2 and 5, cephalopods; 7, 8, and 9, 
corals. 
(1, Strophomena alternata; 2, Trocholites ammo- 
nius; 3, Orthis sinuata; 4, Strophomena alter- 
nata; 5, Orthoceras amplicameratum ; 6, Lingula 
quadrata; 7 and 8, Chaetetes dalei; 9, A cup 
coral; 10, Orthis lyrix.) 
preserved in these 
ancient strata. The 
plantsare all of low 
forms, and the ani- 
mals are of types 
lower than the 
insects. Nothing © 
higher than this 
is known from the 
rocks of this time. 
Silurian Life. — 
In the Silurian 
great progress in 
the history of life 
on the globe is 
made. The trilo- 
bites of the ocean, 
which were domi- 
nant in the Cam- 
brian and Ordovi- 
cian times, have diminished very decidedly; but the 
brachiopods and corals have continued to increase in 
importance and variety, and crinoids or sea-lilies have 
developed remarkably (Fig. 241). 
These beautiful 
