STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 145 



signify that a coal seam in process of formation was exposed. Local 

 conglomerates in many sandstones occupy the channelways of rapid 

 streams ; local unconformities between sandstone and shale suggest 

 changes in direction of drainage. The coal seams themselves ap- 

 pear to have been subjected to subaerial erosion and to have been 

 traversed by streams as in modern swamps. " Horsebacks " or 

 " rolls " of the roof have been found wherever extensive mining 

 operations have been carried on. They mark channel ways of 

 varying width and depth, now filled with material like that of an 

 overlying deposit; sometimes the material is the same with that 

 forming the immediate roof, in which case the stream was probably 

 contemporaneous with the bog; but not infrequently the channel- 

 way was excavated after the roof had been deposited. The condi- 

 tions are commonplaces in modern deposits. 



5. Soils of Vegetation. — Reports on areas of Cretaceous coal m 

 North America give few instances where soils of vegetation have 

 been observed in the rocks between coal seams. One must not for- 

 get, in this connection, that, generally speaking, observers have been 

 compelled to depend on natural exposures, which are imperfect, and 

 that the work has been done at cost of much personal discomfort. 

 But the few illustrations available show that the condition is less 

 rare than the record shows. A dense growth of Sphenoptcris, in 

 place, has been reported from the Wealden of England and a similar 

 growth of Eqitiscfum from that of Hannover. A grove of large 

 trees exists in the Upper Cretaceous of Queensland, clearly in place 

 of growth, where they were buried by drifting sand ; an ancient 

 soil in New Zealand contains roots in place. The Upper Cretaceous 

 of Greenland has bands with ferns, conifers, dicotyledons, erect 

 stumps and silicified wood. An old soil was seen on Pine River 

 of Alberta in the Lower Kootenai, which contains erect stems, evi- 

 dently in the place of growth. 



6. The Roof of Coal Beds. — Coal seams may have shale, clay, 

 sandstone ,or limestone as the roof. In parts of some mines one 

 finds shale as roof in one part, but sandstone in others ; the varia- 

 tion being due, apparently, to local removal of the shale during or 

 prior to deposition of the sandstone. It may be marine limestone or 

 a detrital deposit containing marine fossils. Occasionally, a parting 



