ALLUVIAL DIVISION. 
Ill 
Subterranean Streams. 
These-are not uncommon in limestone regions. All rocks near the surface of the earth are 
intersected by fissures; and into these, the surface waters necessarily find their way, and 
remain, unless they communicate with the surface of the earth, or a porous soil at a lower 
level, so as to form springs. In limestone rocks, these fissures become wider in consequence 
of the solvent action of the Avater, if it flows through them ; and the waters of many of these 
fissures uniting, have a common outlet, and,thus form small or large springs. Sometimes many 
square miles are thus drained by one spring, and a large stream sufficient for mills, and some¬ 
times for navigation, flows from a single fountain. In limestone regions, springs and streams 
are less numerous on the surface, than where other rock formations predominate, because 
the waters mostly flow beneath the surface through the fissures of the rocks, but the springs 
are copious. Streams in such districts sometimes disappear by flowing into the fissures or 
caverns, and rise again at a greater or less distance as large springs. These are called subter¬ 
ranean streams. Streams thus pass under mountains and hills by natural tunnels. Exten¬ 
sive caverns are thus formed by subterranean streams ; and as they become very broad, the 
rock is sometimes insufficient to support the sviperincumbent weight, and it sinks in from the 
surface of the earth, forming sink-holes and valleys; and if the sunken space be large, the 
stream enters at one extremity, and disappears at the other. If they are not large, they are 
called sinking springs. 
Natural bridges cover short canals of subterranean streams, where the rock that once 
covered them has nearly all fallen into the caverns below, and left the stream open to the 
heavens in a deep ravine, except the small portion which remains to form the bridge. 
Limestone Springs. 
In Rockland county, a limestone ^spring has been already mentioned as a gaseous spring.* 
In Columbia county, the New-Lebanon springs h^ve also been mentioned t under the same 
head of Gaseous springs. 
The city of Hudson is supplied with water from a limestone spring, on the northwest base 
of Becraft’s mountain. Another spring emerges from the eastern base, and the water was 
warm when it was examined in the summer season. It lasted like brook water, and is sup¬ 
posed to be the outlet of a small brook that sinks into the fissures of the limestone, in a sink¬ 
hole on the top of the mountain. 
Near the line of Canaan township, a small stream sinks near the limestone, and reappears 
at a distance of a quarter of a mile, on the land of Mr. Lord. 
Cold spring, southwest of Stessing mountain in Dutchess county, flows from the base of a 
limestone ridge. A brook flows from it large enough to carry a mill. It is generally reputed 
Vide page 107 of this volume. 
t Vide page 105. 
