40 



COAL FORMATION. 



existing species in the number of their eyes ; fresh-water mollusks, 

 and very remarkable fishes, which, in certain respects, resembled 

 reptiles, and had their bodies covered by thick solid plates. 



7. The debris of the plants of that period, accumulated in im- 

 mense masses and altered by time and other causes, were trans- 

 formed into the combustible material, which is so immensely 

 valuable, known under the name of coal. 



8. The deposits of coal begin, in France, ordinarily with pud- 

 ding-stones formed of the debris of different rocks from the sur- 

 rounding country, often comprising gigantic blocks scarcely rounded. 

 Sometimes finer pudding-stones alternate with sandstone, which 

 always constitutes a chief part of the deposit. Very numerous va- 

 rieties of these sandstones, arising from the size of the grains of 

 quartz and the quantity of argilla'ceous matter entering into their 

 composition, are found ; they are frequently micaceous and schistose ; 

 ;hey contain beds of clay-slate and bituminous schist, which are 

 sometimes very thick, but rarely calcareous strata. The masses 

 of coal are scattered throughout, but are always separated from the 

 sandstone by beds of slate ; these are at first nearly pure, then 

 mixed with the combustible, and finally are represented alone above 

 the deposit. 



9. Besides the coal formed by the accumulation of the debris of 



decomposed plants, the coal-measures con- 

 tain a great number of the remains of 

 plants which retain their organic charac- 

 ters : the stems and trunks of trees are 

 found in the sandstone; the leaves have 

 left their imprints perfectly preserved in 

 the schists and clays which accompany 

 the coal. 



10. The impressions of ferns are ex- 

 tremely numerous ; among them is the 

 Pecopferis ( t fig* 37), of which the leaflets, 

 but little detached from the pedicle, are 

 joined in a single ieaf, deeply incised, in 

 which we iecognise a principal nervure, 

 from which the secondary nervures arise 

 perpendicularly ; the Sphscnopteris (fg. 

 38), analogous to the preceding, but in 

 which the leaflets are moie distinct, deeply 

 lobed, and have the nervures radiate al- 

 most from the base ; the Neuro'pteris 

 a ls has the leaflets de- 



(t. What animals existed at that period? 



7. From what, was coal formed ? 



8. In what kind of rock is coal found ? 



9. In what do we find impressions of plants ? 



