312 



PALEOZOIC TIME. 



Feet. 



18. Shale ; thickness considerable ? 



19. Shaly sandstone 30 



20. Red and blue calcareous marlytes 20? 



21. Coal No. G 1 



22. Limestone fossiliferous 2 



23. Slates and shales 100 



24. Gray clayey sandstone 70 



25. Redmarlyte 10 



26. Shale and slaty sandstone 10 



27. Limestone, non-fossiliferous 3 



28. Shales 32 



29. Limestone . 2 



30. Red and yellow shale 12 



31. Limestone 4 



32. Shale and sand 30 



33. Limestone, with bands of spathic IRON-ORE .... 25 



34. Pittsburg Coal, No. H 8, 9 



In other regions the succession is widely different. The rocks are 

 distinguished from those of other ages, not by their colors or kinds, 

 nor by their succession, but by the species of fossil plants and animals 

 they contain. 



The Coal beds are thin, compared with the associated rock strata, 

 usually not exceeding one-fiftieth of the whole thickness. 



The rock underlying a coal bed may be of either of the kinds men- 

 tioned ; but usually it is a clayey layer (or bed of fine clay), which 

 is called the under-clay. Being frequently suitable for making fire- 

 brick, such beds often go by the name of fire-clay. This under-clay 

 generally contains fossil plants, and especially the roots or under-water 

 stems of Carboniferous plants, called Stigmarice, and it is often called 

 the old dirt-bed, or the bed of earth over which the plants grew that 





Fig. 614. 





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Section of Coal-measures 



at the Joggins, Nova Scotia (with erect stumps in the sandstone, and 

 rootlets in the under-clays) 



commenced to form the coal-bed. It is either this, or the clayey bot- 

 tom of the plant-bearing marshes or lakes. In some cases, trunks of 

 trees rise from it, penetrating the coal layer and rock above it. 



