46 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



and they lie prostrate in intervals between the rooted stumps. 

 Henslow saw, at the Portland locality, root-shaped cavities descend- 

 ing into the rock underlying the dirt bed. Equisetiform plants in 

 vertical position and rooted in place of growth occur at several 

 horizons in the Lower Oolite and the Lias in Yorkshire. Calamites 

 and Equisetum, in erect position, are found in beds above and below 

 seams of coal at numerous localities within the Richmond field. 

 These ancient soils, with erect stems in place, would seem to indi- 

 cate land surfaces at various times during deposition of the coal- 

 bearing deposits. 



As in the newer formations, the roof may be sandstone, shale 

 or limestone ; it may contain marine or freshwater forms. At 

 Brora in Scotland, it is a mass of marine shells with quartz sand 

 and carbonaceous materials, bound together by a calcareous cement ; 

 it passes downward into coarse coal — a faux-toit. Marine shells are 

 present in the roof of at least one seam in the Fiinfkirchen district 

 and bituminous limestone rests on the coal at some localities near St. 

 Anton in Austria. The ordinary roof is sandstone or shale, one 

 or the other predominating in different areas ; not infrequently it is 

 sandstone in one mine but shale in another nearby. Finely lami- 

 nated sandstone is not rare. Roof shales are often very rich in 

 plant remains, leaves being especially well-preserved, as though they 

 had been lifted gently from the surface of the bog by muddy water. 

 The sandstone roof of the Lettenkohle in Unterfranken is an old 

 soil, containing erect roots. 



Frequently, the passage from good coal to roof is gradual and 

 this is equally true of the passage from coal to the floor, there being 

 distinct faux-toit and faux-mur ; but, at times, the passage is 

 abrupt. Occasionally, the character of the coal changes in such 

 manner as to suggest that one portion of the seam sank below drain- 

 age while the other remained above it ; the " Kimmeridge coal " in 

 the typical area is merely a rich carbonaceous shale, whereas in Wilt- 

 shire it resembles peat. In the Tchoulym field of Russia, the burial 

 must have been abrupt, for the upper portion of the coal is very 

 peat-like at some localities. Coal seams, more than 2 feet thick, are 

 rarely single, but are divided into benches by partings of sandstone 

 or clay, often containing much mineral charcoal. These vary much 



