344 
SINKING OF THE SOIL. 
thus constructed, it is observed that the ground defended by 
the more ancient embankments is lower than that embraced 
within the newer enclosures, and this depression of level has 
been ascribed to a general subsidence of the coast from geo¬ 
logical causes ; but the better opinion seems to be that it is, in 
most cases, due merely to the consolidation and settling of the 
earth from being more effectually dried, from the weight of 
the dikes, from the tread of men and cattle, and from the 
movement of the heavy wagons which carry off the crops.* 
* The shaking of the ground, even when loaded with large buildings, 
by the passage of heavy carriages or artillery, or by the inarch of a body 
of cavalry or even infantry, shows that such causes may produce important 
mechanical elfects on the condition of the soil. The bogs in the Nether¬ 
lands, 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 an¬ 
cient trees rise of themselves to the surface. Staring ascribes this singular 
phenomenon to the agitation of the ground by the tread of cattle. “ When 
roadbeds,” observes he, “ are constructed of gravel and pebbles of differ¬ 
ent 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 carriages 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 .”—Be 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 sur¬ 
face, new pebbles, and even bowlders 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 
uncommon 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 popu¬ 
larly 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 prevented from sinking as low as before bv loose earth which 
