676 THE WONDERS OF GEOLOGY. Lect. VII. 



to explain the successive submergence of so many forests 

 which grew one above the other, may have enabled this 

 enormous mass of strata to have accumulated in a sea of 

 moderate depth."* 



In Lehigh Summit mine, there is a bed of anthracite 

 fifty feet thick, with no interpolated detritus except two 

 thin layers of clay with stigmarise. Mr. Lyell considers it 

 difficult to explain such an accumulation of pure vegetable 

 matter, upon the hypothesis of the trees having been 

 drifted, but intelligible, if we suppose them to have grown 

 on the spot : yet he infers that to produce such a layer of 

 coal, the original mass of vegetables must have been 

 between three and four hundred feet in thickness ;"j*— but 

 where are there any indications of the soil on which such 

 forests grew ? 



12. COAL-SHALES AND VEGETABLE REMAINS. 1 have 



already stated that it is the shales, or slaty coal of the roof, 

 from which the most abundant and illustrative examples of 

 the plants of the carboniferous epoch are obtained ; in many 

 layers, vegetable remains occur between every lamina, the 

 entire mass being formed of carbonized leaves and stems, 

 closely pressed together in clay. The carbonaceous matter is 

 sometimes in an unconsolidated state, exhibiting the mat- 

 ted fibres, leaves, and stems. This condition, indicating 

 an intermediate stage in the formation of coal, is not of 

 unfrequent occurrence in the upper secondary and tertiary 

 carbonaceous deposits, but is rare in the most ancient J 



The roof of a coal-mine when newly exposed displays 

 the most interesting spectacle imaginable ; leaves, brandies, 

 and stems of the most elegant and delicate forms, being 

 embossed on the dark shining surface. The coal-mines 

 of Bohemia, the fossil plants of which are well known, 

 from the beautiful work of Count Sternberg, are stated 



* Travels in America, p. 190. + Ibid. p. 85. 



X Silurian System, p. 100. 



