ALLUVIAL DIVISION. 
37 
mountain side, crushing and bearing down every thing in their paths. In the winter of 1834, 
a large mass was burst off from a high cliff near West-Point, in the Highlands, by the frost, 
and fell with a report almost like thunder, and a jar like a slight shock of an earthquake, 
succeeded by a rumbling noise, caused by the rolling masses as they were precipitated down 
the mountain side. 
Another fall, and from a similar cause, occurred a few years before the preceding, on the 
southeast side of Butter hill in the Highlands, from the face of a nearly vertical cliff. Many 
of the fallen rocks have been split up as a quarry stone, and used in building, and in the 
public works at fortress Monroe, and the Delaware breakwater. The masses still remaining, 
must weigh several thousand tons. 
An observer may perceive hundreds of examples in the Highlands, where similar causes 
have produced the same effects. In fact, all the natural causes, affecting the geological 
structure of the earth, except mineral springs and volcanic action, tend to transfer matter 
from a higher to a lower level. 
Disintegration. 
The causes of alluvion belong to two great classes, viz, mechanical and chemical. The 
tendency of all rocks is to disintegrate and decompose, by the alternate action of heat and 
cold. Rocks that were angular, gradually lose their sharp edges, and become more or less 
rounded; and the soil of gravel, sand, loam or clay, resulting from this change, is partly 
washed or blown away by moving masses of water or by wind ; and the general result is, 
that the land is constantly undergoing a state of degradation in some places, while the others 
are successively raised higher by the accumulated detritus deposited upon them. 
The change of temperature is one great reason of the destruction of rocks. These masses 
are imperfect conductors of caloric ; and the surface being heated or cooled more than the 
other parts of the mass, it undergoes a corresponding change of dimensions, and this with 
such force as to crack the rock. If, for instance, the surface be heated, it expands while 
the other parts remain stationary; but as stones are not elastic, and the force required to 
crush the expanding particles is greater than than required to crack it, the latter result fol¬ 
lows. This principle is often employed in some parts of Europe, and even in this country, 
for splitting rocks, by building a fire on them, instead of using gunpowder. It is also em¬ 
ployed in mines, where the rock is too hard to be drilled for blasting. This principle may 
be well illustrated it in a thick-bottomed glass bottle or tumbler; if it be suddenly heated by 
putting in hot water, a crack or fissure in the glass, from the unequal expansion, is the almost 
inevitable consequence. 
Again, in the winter season, the water that has filtered into the fissures produced by 
changes of temperature, freezes, and by its expansion opens the fissures still wider. ^ All have 
seen the slope of fragments at the base of every rocky cliff, and many have heard or seen 
masses of rock tumbling down the mountains, loosened from their places by this cause. The 
annexed diagrams illustrate the above effects, in examples observed by myself: 
