84 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



is accompanied by iron ore. The coal beds, though variable, are 

 wonderfully persistent and are always associated with fireclay. 

 There is no haphazard mode of occurrence. Coal is product of land 

 life; limestone is of marine origin; the ore depends on life for con- 

 centration ; sandstone, occupying the intervals between other rocks, 

 is due to inorganic forces and it may be about equivalent to the 

 others. Orton's conclusions based on more than twenty years of 

 study in much of the Appalachian basin, are: 



(i) The Ohio coal-field, at the beginning of the Carboniferous, 

 was an arm of the sea with the Cincinnati arch as the western boun- 

 dary. (2) Marginal swamps of varying width became the earliest 

 coal seams by long continued growth and subsequent fossilization. 

 (3) While the swamps were submerged, in succession, and covered 

 by shale, sandstone or limestone, in turn covered by other swamps, 

 the continental nucleus grew slowly at the south and the Cincinnati 

 arch united with it by like advance eastward, expelling the waters 

 of the gulf and converting the earlier formed portions of the coal 

 formation into dry land. (4) Every coal swamp had a narrower 

 area than its predecessor. (5) As all coal seams were formed at 

 sea level, so all were raised by continental growth to an approximate 

 equality, which their outermost outliers still retain. (6) To look 

 for the earlier formed seams in the center of the basin would be 

 to look for the living among the dead. (7 ) In the formation of one 

 seam, in particular, the floor of the gulf, around which the swamps 

 were growing, seems to have been raised nearly to sea level at many 

 points, and coal appears to have been formed in island-like masses 

 over much wider areas than any single marginal swamp would 

 account for. 



Bolton^''" describes a peculiar deposit of coal in Ireland. The 

 Jarrow coal bed appears to be a great cake, attaining a maximum 

 thickness of 16 feet and thinning in all directions except toward 

 the west, in which direction no tests have been made. I'nderclay is 

 absent at almost all localities. The lower part of the deposit is a 

 smutty anthracite with slaty structure and containing abundance of 



"Mf. ]'>i)llnn, " Notes on tlio Plant and Fisli remains from the Jarrow Col- 

 liery, Co. Kilkenny," Trans. Manchester Gcol. Soc, Vol. XXII., 1894. 



84 



