ALLUVIAL DIVISION. 
39 
There is no rock which, if carefully examined after long exposure, does not show some 
traces of atmospheric action : the hardest siliceous rocks even show it. The effect of atmo¬ 
spheric action on cliffs of sandstone, in which the cement is of various degrees of destructi- 
bility, giving them such romantic and fantastic forms, is well known. 
Crystalline limestone, from losing the cement that connected the grains, sometimes crum¬ 
bles to sand. An example of this occurs near Sing-Sing, where the sand was at first used 
to mix in mortar for building, under the impression that it was siliceous sand. The building 
tumbled down, from no adhesion taking place. The white and dolomitic limestones of the 
counties of New-York, Westchester, Putnam and Dutchess, may be said to be characterized 
by crumbling on the surface by long exposure. In many localities they do not thus crumble, 
but very generally they are covered by materials derived from their own disintegration. 
Causes of Disintegration. 
There are several causes, which may act singly or conjointly, to produce a disintegration 
or crumbling of a rock. 
1. Water may act so as to dissolve the cement which holds the grains of some rocks to¬ 
gether, or one of the constituents of the rock. 
2. Water, by means of various substances which it holds in solution, tends to decompose 
some one or more of the constituent minerals of various rocks, to form new combinations. 
Gneiss and granite frequently crumble to gravel, by the decomposition of the contained feld¬ 
spar, and the rain and spring waters remove the potassa in the state of carbonate or sulphate. 
3. The change of composition effected by atmospheric agents, as the change of oxidation of 
iron from a proto to a peroxide, for example, in basalt and trap ; the decomposition of pyrites 
swelling and splitting the stone, and the excess of sulphuric acid resulting, acts as a decom¬ 
posing agent upon other minerals in the rock. 
Transport by floating ice. 
Bakewell, in his Introduction to Geology, remarks, “Vast masses of rock near the sea¬ 
shore are sometimes enveloped in fields of ice, and raised up and transported to foreign countries. 
Ice is specifically lighter than water; every cubic yard will support a stone of one hun¬ 
dred pounds weight; hence we must not be surprised at the insulated rocks of granite that are 
sometimes found in situations far remote from primitive mountains. These blocks have been 
floated over the ocean, and their angular points and edges defended from attrition during their 
passage by the surrounding ice.” 
Dr. Hayden gives the following example, as coming under his own observation : 
In the winter of 1780, memorable as the hard winter, and well remembered by many of the aged as the 
most severe since their recollection, the ice was frozen to a great thickness and solidity: in many places 
the water was literally frozen to the bottom. In the month of January, as usual, there came a great and 
