50 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 



mosses cannot begin on inorganic material. This material can 

 hardly be determined satisfactorily either positively or negatively, 

 as the thickness of the organic layer is regarded as immaterial, one 

 author holding that it may be so thin as to be unrecognizable, while 

 he still insists that it must be present. There can be no doubt 

 that, when a Hochmoor increases by transgression, it is likely to 

 rest in part upon inorganic material. Rohhumus on bare rock, the 

 sphagnum-peat described by Dachnowski and some instances to be 

 noticed on a later page appear to indicate that a moss peat may 

 begin on inorganic surfaces. At the same time, it is beyond all 

 question that, of deposits originating on the surface of plains, a 

 very considerable proportion began on forested areas, where the 

 litter afforded excellent base for peat growth after the drainage had 

 been impeded. Shaler, many years ago, referred to transgressing 

 bogs in New England, which invaded forests and eventually killed 

 even the water-loving trees. Lewis** says that in the lowland 

 mosses of Wigtonshire, Scotland, the till surrounding the original 

 area of obstructed drainage carried birch and CaUima, which were 

 replaced gradually by hazel and alder. In these deposits, Betula is 

 abundant even on the floor. Sanford regards the Everglades of 

 Florida as due chiefly to impeded drainage. Peat operators have 

 long known that if the bog be stripped clean to the underclay, peat 

 growth begins very much more slowly than when a thin cover of 

 vegetable matter has been left on the clay. 



The partings in peat deposits, when consisting of clay, sand or 

 marl, indicate subsidence or flooding. They may be so numerous 

 as to render the mass worthless, the laminations of peat and foreign 

 matter being alike thin ; or there may be alternations of fairly clean 

 peat with layers of intimately mingled organic and inorganic ma- 

 terials. The former indicate very frequent floodings, while the 

 latter tell of a long period of subsidence interrupted by longer or 

 shorter periods of comparative stability. A good illustration of the 

 latter condition is that given by Debray*^ in his description of a 



44 F. J. Lewis, " The Plant Remains in the Scottish Peat Mosses," Pt. I., 

 Trans. Roy. Soc. Edinb., Vol. XLL, 1906, pp. 699-722. 



45 L. Debray, " fitude geologique et archeologique de quelques tourbieres 



