38 STEVENSON— FORMATION OF COAL BEDS. [April 18, 



The floor is uneven, characterized by " hiUs " and " swamps," the 

 coal being 4 to 5 feet thick in the latter but thinning away to almost 

 nothing on the former, which are merely piles of pebble rock, rising 

 at times with a slope of 15 degrees. The " swamps " are depressions 

 among the " hills," which White thinks are due to erosion, as the 

 pebble rock varies from 6 to 25 feet, the least thickness being under 

 the swamps. This condition occurs less commonly in higher beds, 

 but it is by no means rare. The Lower Kittanning, in Lawrence 

 county, rests on an uneven floor of fireclay which has an extreme 

 thickness of 10 feet. The coal often dips into swamps with increased 

 thickness at the rate of one foot to the yard; it decreases usually 

 about one half on the hills. The reports by Chance and W. G. Piatt 

 note similar conditions in other coal beds of the Allegheny; these 

 are only too familiar in the Conemaugh. 



Are Coal Beds Continuous? 



The query at once presents itself, are these petty areas excep- 

 tional or are they typical? They are from a few yards to several 

 miles in diameter, and one might expect to find yet larger areas, dis- 

 tinctly limited. The question is of great economic importance and 

 the answer is of equal importance in relation to the problem in hand. 

 Are coal beds continuous or do the names applied to them designate 

 only horizons, marking periods when accumulation of coal took 

 place, so to say, contemporaneously at many places and in extensive 

 areas ? 



The question has been raised less frequently in Europe than in 

 the United States because the coalfields are of comparatively small 

 extent. But in the bituminous region of the Appalachian general- 

 izations presented long ago still hold in the nomenclature, though 

 some observers have opposed them strenuously. The early surveys 

 were made when the region was thinly settled, when mining opera- 

 tions were unimportant and exposures of coal beds were mostly in 

 small pits opened for local supply. There were few records of 

 shafts, there were no records of borings and there were few graded 

 roads ; the section was worked out laboriously from natural ex- 

 posures and without aid of the instruments now regarded as an 



