1913.] STEVENSON— FORMATION OF COAL BEDS. 161 



ceous shale being continuous, from the chemist's point of view. So 

 with peat, for one may find clean peat with little ash passing gradually 

 intoordinary mud within a niile or less. Coal at times has very much 

 less ash than was contained in the plants whence it was derived ; the 

 same is true of peat, which, as a commercial product, has from i to 

 20 per cent. But sphagnum has from 3 to 4 per cent., yet Vohl 

 analyzed a sphagnum peat which contained only 1.25 per cent, of ash. 



Coal beds are buried deeply under detrital deposits ; but those 

 deposits were laid down, one at a time. Peat beds are of late- 

 Quaternary or Recent age ; opportunity for deep burial has come to 

 few of them. But buried bogs are a familiar phenomenon and in 

 some cases the cover is thick. At one locality in Ohio, a bed, 15 to 

 20 feet thick, underlies 90 feet of sands and gravels ; in Indiana, one 

 bed, 2 to 20 feet thick, has been found underlying a considerable 

 area at a depth of 60 to 120 feet. The buried peats of Scotland, 

 France, Germany, Holland, Switzerland, equally with the buried 

 cypress swamps of the Mississippi region and the great buried swamp 

 of the Ganges area, all afford proof that it is not the necessary fate 

 of peat bogs, in situ, to be destroyed by oxidation. 



The extent of modern peat deposits compares very favorably 

 with that of coal beds ; that, extending across Belgium from Holland 

 into France, equals the extent of the Pittsburgh coal bed as it exists 

 to-day. The upper peat bed of the Gangetic plain seems to have 

 been proved in an area of nearly 2,800 miles, exceeding that of any 

 American coal bed except the Pittsburgh and two in the Middle 

 Pottsville. The Alaskan tundra has much greater continuous areas 

 and at some localities the thickness is very great. 



Coal beds frequently divide and in some cases the divisions re- 

 unite. Peat deposits do the same, as Lorie's records show. True, 

 the divergence of peat benches is not so remarkable as that observed 

 in some coal beds but otherwise the condition is the same ; at times, 

 the origin of other features is suggested. The irregular subsidence 

 of the New Madrid region on the Mississippi affected an area of 

 rather more than 2,000 square miles ; when that depressed region 

 has been filled up by silts and overspread by a new swamp, division 

 and re-union will be as distinct as it is in the Alammoth coal bed. 



