110 PROBABLE ANTIQUITY OF PEAT. CHAP. vir. 



peat, enclosing trunks of flattened trees, have been thrown 

 up on the coast at the mouth of the Somme; seeming to 

 indicate that there has been a subsidence of the land and a 

 consequent submergence of what was once a westward con- 

 tinuation of the valley of the Somme into what is now a 

 part of the British Channel, or La Manche. 



Wbethcr the vegetation of the lowest layers of peat difiPered 

 as to the geographical distribution of some of the trees from 

 the middle, and this from the uppermost peat, as in Denmark, 

 has not 3^et been ascertained; nor have careful observations 

 been made with a view of calculating the minimum of time 

 which the accumulation of so dense a mass of vegetable matter 

 must have taken. A foot in thickness of highl}- compressed 

 peat, such as is sometimes reached in the bottom of the bogs, 

 is obviously the equivalent in time of a much greater thick- 

 ness of peat of spongy and loose texture, found near the sur- 

 face. The workmen who cut peat, or dredge it up from the 

 bottom of s\vam])s and ponds, declare that in the course of 

 their lives none of the hollows which Ihej' have found, or 

 caused by extracting peat, have ever been refilled, even to a 

 small extent. They deny, therefore, that the peat grows. 

 This, as M. Boucher de Perthes observes, is a mistake; but it 

 iin|)lies thai the increase in one generation is not very appre- 

 ciable by the unscientitic. 



The antiquary finds near the surface Gallo-lloman remains, 

 an-d still deeper Celtic weapons of the stone period. But the 

 depth at which lioman works of art occur varies in different 

 places, and is no sui'e test of age ; because in some parts of 

 the swamps, especially near the river, the peat is often so fluid 

 that heavy substances may sink through it, carried down by 

 their own gravity. In one case, however, M. Boucher de 

 Perthes observed several large flat dishes of Eoman pottery, 

 lying in a horizontal position in the peat, the shape of 

 which must have prevented them from sinking or penetrating 



