176 THE TAUIS OF THE ANCIENT WORLD. 



3. Ihe Carboniferous strata, (mountain 

 limestone and coal.) 



4. The Permian group, (lower new red sand- 

 stone, etc.) 



5. The Triassic strata, (upper new red sand- 

 stone, etc.) 



G. Oolite and Lias. 



7. Wealdeu beds. 



8. Chalk. And finally, 



9. The Tertiary strata. 



The earlier strata (the silurian and old red 

 sandstone) contain but few traces of vegetable 

 life, at least as far as researches have at present 

 shown, and these are principally Algce, or sea- 

 weeds. But in the carboniferous group of 

 strata the remains of land plants are extremely 

 abundant. Not only is coal itself a mass of 

 ATgotable matter — altered, it is true, by burial 

 under high pressure, and perhaps much lieat — 

 but it still retains, in many cases, the very 

 form and structure of the original vessels, as 

 can readily be seen when very thin slices are 

 placed under the microscope. The beds of 

 shale (hardened mud) which generally accom- 

 pany and alternate with the strata of coal, ai-e 

 full of the leaves of plants and fronds of ferns, 

 which are displayed in beautiful preservation 

 on the blabs which are raised in working the 



