STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 75 



reed and brown moss peat are shown. Well-marked Bruchtorf 

 follows, composed mostly of Fichte, though occasional specimens of 

 Scotch fir and birch were seen. According to Zailier, the sedge- 

 moss peat follows, but Schreiber saw only a mere fragment of it. 

 The deposit underlies moraine stuff. The Hopfgarten peat is less 

 like coal than that at Piehl, though both are of the same age. 

 Schreiber explains this by difference in the pressure. 



Bursting Bogs. — Peat often remains a long time in the condition 

 of " quaking bog." The floating mat constantly increases in thick- 

 ness, so that at length it can carry large trees ; but, under it, material 

 from the bottom of the mat accumulates slowly and is pulpy. After 

 long-continued rains, water may collect in such quantity as to break 

 the cover and the black mud may be discharged upon lower levels. 

 Lyell,^'' referring to the Solway moss in southern Scotland, states 

 that its surface, covered with grass and rushes, shakes under the 

 least pressure, the bottom being unsound and semi-fluid. On De- 

 cember 1 6, 1772, having been filled like a sponge during long-con- 

 tinued heavy rains, this bog swelled above the surrounding area and 

 finally burst. A stream of half consolidated black mud crept over 

 the plain with speed like that of an ordinary lava-current. The 

 deluge covered about 400 acres. Tait^''' says that a very great part 

 of the moss of Kincardine is a quaking bog, the peat being so wet 

 as to be semi-fluid. During the process of reclamation, the support 

 for the mass was removed and, on March 21, 1792, the peat began 

 to run on the west side and the flow covered about an acre. On the 

 same day in 1793, the flow was repeated and the peat mud covered 

 nearly 12 acres of the cleared space. The extreme depth of the 

 overflow was 8 feet. 



The phenomenon is by no means rare. Lyell conceives that 

 lakes and arms of the sea must occasionally become receptacles of 

 drift peat ; and in this way he would explain alternations of clay 

 and sand with deposits of peat, found frequently on some coasts. 

 This explanation would sufifice only for some indefinite and in- 

 significant deposits ; it is difficult to conceive how the required con- 



^6 C. Lyell, " Principles of Geology," New York, 1872, Vol. II., pp. 510, 511. 

 9^ C. Tait, " An Account of the Peat-Mosses of Kincardine and Flanders, 

 Perthshire," Trans. Roy. Soc. Edinburgh, Vol. III., 1794, p. 278. 



