36 
GEOLOGY OF THE FIRST DISTRICT. 
mile from the bridge. During the night, about half or throe quarters of an acre of ground 
slid forward into the creek, and pushed up a large bank of sand on the opposite side. The 
slidden ground sunk twenty-two feet below its former level. The substratum is a very sapo¬ 
naceous blue clay; and being undermined either by the stream, by land springs, or lying on 
the inclined slate rock, which seems most probable, slid to its present position. The clay is 
broken up and contorted in various ways, showing the lateral pressure to which it has been 
subjected. It occurred very near a house, and the underpinning of a barn on one side was 
carried away. Apple and other trees still grow and flourish as they did when the ground on 
which they stand was on a higher level. More of the land, of a rod or two in width, has 
slidden down since the first sinking of the mass. 
Land slips are common in the clay beds between Hudson and Merino mountain, and in 
fact throughout the whole of this quaternary formation, where the action of streams, the sea, 
or other causes natural or artificial, have repeatedly exposed high banks of the clay, sand and 
gravel throughout the valleys of the Hudson and its tributaries, and the coasts of Lake Cham¬ 
plain, of Long, Staten and other islands in the First Geological district. The local examples 
known are too numerous to mention, and are of little interest more than their general results, 
viz. the degradation and washing away of these materials, to be deposited in some other 
locality. 
Some examples of the sinking down of limestone rocks into caverns below, in consequence 
of the gradual removal of the limestone that supported the roofs of the caverns, by the solvent 
and erosive action of subterranean springs and streams, are here introduced. 
Near Round pond, four miles southwest of West-Point, Orange county, the ground sunk 
down several feet, while Mr. Cronkite, the owner of the land, was digging a pit to bury 
potatoes for the winter. The subjacent rock was the white and flesh-colored limestone that 
occurs in that region, highly crystalline, and containing crystals of spinelle, augite, horn¬ 
blende, phosphate of lime, brucite, hexagonal crystals of mica, etc. The fall of the rock 
exposed a cavern extending thirty or forty feet from the pit-fall, to which distance I explored 
it in various directions in 1825. The roof was studded with minute brilliant crystals of these 
various minerals. The cavern is nearly filled up since that time by wash, and by carting 
stones from the grounds around to prevent cattle from falling into it. 
Another example occurred near Barnegat, Dutchess county, where the ground sunk, from 
the rock being no longer able to support the weight of the superincumbent mass. A man 
ploughing had passed over the ground that sunk, but a moment before. 
Another occurred near Pine-Plains, on the line of a subterranean stream. Trees were not 
disturbed in their growth on the sunken ground; but a cow that was on it, died for want of 
water and food, from her inability to climb out of the sunken space. 
The expansion of water, as it freezes in the fissures of rocks and cliffs, acts with irresisti¬ 
ble force, detaching large blocks, which are daily falling in the winter and spring. In Green¬ 
land, the noise of such falls is said to resemble thunder. 
Every one who has lived in a mountainous region, where high cliffs were near, must often 
have heard, if not seen, the enormous masses of rock tumbling and thundering down the 
