SINKING OF THE SOIL. 403' 



men and cattle, and from the movement of the heavy wagons 

 which carry off the crops.* Notwithstanding this slow sinking, 



* The shaking of the ground, even when loaded with large buildings, by 

 the passage of heavy carriages or artillery, or by the march of a body of 

 cavalry or even infantry, shows that such causes may produce important 

 mechanical effects on the condition of the soil. The bogs in the Nctlierlands, 

 as in most other countries, contain large numbers of fallen trees, buried to a 

 certain depth by earth and vegetable mould. When the bogs are dry enough 

 to serve as pastures, it is observed that trunks of these ancient trees rise of 

 themselves to the surface. Staring ascribes this singular pheuomeuon to the 

 agitation of the ground by the tread of cattle. " When road-beds," observes 

 he, "are constructed of gravel and pebbles of different sizes, and these latter 

 are placed at the bottom without being broken and rolled hard together, they 

 are soon brought to the top by the effect of travel on the road. Lying loosely, 

 they undergo some motion from the passage of every wagon-wheel and the 

 tread of every horse that passes over them. This motion is an oscillation or 

 partial rolling, and as one side of a pebble is raised, a little fine sand or earth 

 is forced under it, and the frequent repetition of this process by cattle or car- 

 riages moving in opposite directions brings it at last to the surface. We may 

 suppose that a similar effect is produced on the stems of trees in the bogs by 

 the tread of animals." — De Bodem van Nederland, i., pp. 75, 76. 



It is observed in the Northern United States, that when soils containing 

 pebbles are cleared and cultivated and the stones removed from the surface, 

 new pebbles, and even boulders of many pounds weight, continue to show 

 themselves above the ground, every spring, for a long series of years. In 

 clayey soils the fence-posts are thrown up in a similar way, and it is not un- 

 common to see the lower rail of a fence thus gradually raised a foot or even 

 two feet above the ground. This rising of stones and fences is popularly 

 ascribed to the action of the severe frosts of that climate. The expansion of 

 the ground, in freezing, it is said, raises its surface, and, with the surface, 

 objects lying near or connected with it. When the soil thaws in the spring, 

 it settles back again to its former level, while the pebbles and posts are pre- 

 vented from sinking as low as before by loose earth which has fallen under 

 them. The fact that the elevation spoken of is observed only in the spring, 

 gives countenance to this theory, which is perhaps applicable also to the cases 

 stated by Staring, and it is probable that the two causes above assigned con- 

 cur in producing the effect. The rising of stones to the surface of fields is 

 observed also m Norway, and is probably due to the same cause. A contrary 

 action is observed in England, and is ascribed by Darwin to the covering of 

 the stones by the casts of earth-ioorms. 



The question of the subsidence of the Netherlandish coast has been much 

 discussed. Not to mention earlier geologists, Venema, in several essays, and 

 particularly in Het Dalen van de Noordelijke Kuststreken van ons Land, 1854, 

 adduces many facts and arguments to prove a slow sinking of the northern 

 provinces of Holland. Laveleye {Affaissement du sol et envasement desfleuve» 

 survenus dans les temps historiques, 1859), upon a still fuller investigation, ar- 

 rives at the same conclusion. The eminent geologist Staring, however, wlic 



