414 ELEMENTARY GEOLOGY 
those that are found are of lower orders. The land 
animals are insects of low types, mainly allied to the 
group of cockroaches, which are the most ancient of 
insects. Scorpions are also present as fossils in the 
Silurian rocks. 
Fic: 237. 
A slab containing many Devonian brachiopods. 
Devonian Life.— In the Devonian, life progressed 
along several important lines. There is very little dif- 
ference between the Devonian marine invertebrates and 
those of the preceding Silurian. Trilobites are slightly 
diminished in number and variety, while brachiopods 
have actually increased (Fig. 237). These interesting 
