38 
GEOLOGY OF THE FIRST DISTRICT. 
Fig. 3. 
Fig. 4. 
Granite vein heaved out of place by frost, Monroe county. Trap and sandstone rock of palisades, with a slope of 
fragments at the base, burst off by the frost. 
Fig. 5. 
Rock split by frost. 
Lightning is a cause, though in a very small degree, of alluvial deposits. It often strikes 
the rocks on mountain cliffs, shivering and tumbling them from their elevated situations into 
the valleys below. 
Chemical agencies acting to decompose some one of the constituents of a rock, generally 
cause it to crumble and disintegrate. Granitic and trap rocks are most liable to this kind of 
disintegration, from changes of composition in the feldspar of one or hornblende of the other. 
The rocking stones, so many of which have been described in our country,* the piles of 
granite blocks in Cornwall, England, the rock basins called the Kettle and Pans, in the Scilly 
Islands, are all the effects of the combined chemical and mechanical causes of atmospheric 
influence. 
* Some in Putnam county are described in the American Journal of Science. 
