64 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 



Sirodot" refers to a locality, where one finds a series of alternating 

 peat and marine deposits, which he explains by supposing that a 

 bar was formed and broken repeatedly, so that the enclosed area 

 was alternately freshwater and marine. 



But this burial comes also to inland deposits, to those on great 

 deltas or at the heads of long estuaries, where the covering ma- 

 terial is of freshwater origin. Much of the Holland-Belgium- 

 France area, in alb more than 7,000 square miles, was not under the 

 sea at any time since the peat began to form ; the great peat bed 

 of the Ganges delta is at 20 to 50 feet below the somewhat irregular 

 surface and is covered with river silts in an area of not less than 

 2,500 square miles. Entombment seems to be the fate of large 

 and small alike. Phillips^*' has recorded the section of the Holder- 

 ness peats, thus: (i) Clay; (2) peat, with plants, trees and roots; 

 (3) variegated clays, with freshwater Lynmcra; (4) peat, like No. 

 2; (5) clay with freshwater Cyclads ; (6) bituminous clay; (7) 

 coarse sandy clay. Number 2 is the persistent member of the sec- 

 tion, but varies greatly in thickness and character. Near Hull, it is 

 30 feet below the surface and 2 feet thick, containing large trees, 

 Buried swamps abound on the Atlantic coast of the United States, 

 especially along streams emptying into the long estuaries occupying 

 " drowned valleys." One citation suffices to illustrate the condi- 

 tions. Berry'^" says that such swamps are exposed by erosion at 

 many places along the James, Rappahannock and Potomac Rivers, 

 all emptying into Chesapeake bay. Most of those observed in 

 1907-09 were cypress swamps, though some were of the open type 

 with birch, oak, pine and other forms. When quiet conditions ac- 

 companied subsidence of the forest bed, clay is the roof, contain- 

 ing Uitio, if the locality be near the head of the estuary, or Rangia 

 cuneata, if farther down within reach of saline water. This condi- 

 tion of quiet subsidence is shown in the photograph of an exposure 



''■5 Sirodot, "Age du gisement de Mont-Dol," etc., Comptcs Rendus, Vol. 

 87, 1878, pp. 267-269. 



76 J. Phillips, " Illustrations of the Geology of Yorkshire," 2d ed., 1835, 

 Vol. I., pp. 25-27. 



'■" E. W. Berry, "Pleistocene Swamp Deposits in Virginia," Amcr. Nat- 

 uralist, Vol. XLIIL, 1909, pp. 432-436. 



