PEAT, OR TURF BOG. 143 



up in the same manner, for now, at low tide, ^e may walk over 

 reefs extending half a league from the shore. But one very im- 

 portant circumstance is, that in many places we find precisely simi- 

 lar deposits, composed of the same species of madrepores, in the 

 interior of land at an elevation of from 200 to 300 yards ; this is 

 seen at Timor, where the deposits are ten or twelve yards thick; 

 at New Holland, Van Diemen's Land, at the Marian Islands. 

 Sandwich Islands, &c., where they rest on argilla'ceous schist, 

 sandstone, limestone, volcanic products, &c. ; in the Isle of France 

 a similar bank, four yards thick, is found placed between two cur- 

 rents of lava. The existence of these deposits in such situations 

 evidently indicates that all these islands have been upheaved from 

 the bosom of the waters, and often at several different periods, for 

 we often find banks of coral at different levels. 



42. Peat, or Turf Bog. There are daily formed, in different 

 excavations of the surface, in valleys of gentle slope, in low and 

 marshy situations, deposits of vegetable matter, the decomposition 

 of which furnishes a combustible called turf or peat, and the 

 mass bears the name of peat-bog. These deposits are formed 

 only under particular circumstances: they are seen only in places 

 where stagnant waters constantly exist, and only in shallow depths; 

 the presence of light is necessary to secure vegetation, to which 

 peat chiefly owes its origin. 



The production of peat, to which all aquatic plants contribute, is princi- 

 pally owing 1 , however, to those which are always submerged, and which 

 multiply rapidly; their debris form the principal paste that envelopes all the 

 others, and probably contributes to their decomposition. A number of ter. 

 restrial plants also, brought to these bogs by brooks, contribute to the forma, 

 tion. Frequently large trees are found buried in the mass, particularly in 

 the lower parts, where they accumulate on sands and clays which form the 

 bottom. Oflen they are seen broken and fallen near the root, which is found 

 attached to the bottom of the hog. In some instances these debris are very 

 numerous, and seem to indicate that entire forests must have been buried 

 on the spot where they grew, before the formation of peat. The plants found 

 in these situations all belong to existing- species ; they are resinous trees, 

 oaks, birch, &c. Remains of mammals are often found in peat-bogs, such as 

 the bones of oxen, the horns of deer, tusks of wild-boars, &c. 



43. Peat-bogs rest on every variety of soil, sometimes even on 

 crystalline rocks; most generally, however, they overlie deposits 

 of sand or clay, and sometimes the rolled flints of the country. 

 There are places where accumulated debris of plants form but a 

 single mass, of greater or less thickness, more compact and blacker 

 at the lower part than in subsequently formed parts of it ; there 

 are other places where the different beds are separated by sedi 

 mentary deposits of alluvium. These are formed of sands, clays, 

 calca'reous or argilla'ceous marls, often containing fresh-water shells 

 in great quantity. Sometimes the surface of the deposit remains 



42. What are peat-hogs ? Of what do they consist? 



43. On what do peat-bogs rest ? 



33* 



