176 
ARTESIAN WELLS. 
^ows through a bed of gravel overlying clay, and the 
porous superstratum is alternately saturated by the 
water of the Thames as the tide rises, and then 
drained again to the distance of several hundred feet 
from the banks when the tide falls, so that the wells 
in this tract regularly ebb and flow. 
We can now understand why water flows out on 
the surface, at the base, or on the side of a hill ; the 
upper strata are porous, while the subjacent are com- . 
posed of clay or other retentive soils. Springs 
which are not affected by long droughts probably 
owe the constancy and uniformity of their volume 
to the great extent of the subterranean reservoirs 
with which they communicate. 
Artesian Wells. — In Artois, in France, a method 
has long been practised of obtaining water by bo- 
ring the earth with a large auger from three to four 
inches in diameter. Hence such wells are called 
Artesian. This practice is founded on the fact that 
there are sheets or veins of fresh water at various 
depths in the earth. When a rock is met with, it is 
triturated with an iron rod, which is alternately ele- 
vated and dropped by machinery ; the materials, thus 
being reduced to a powder, are readily extracted. 
In this manner Mr. Disbrow, at Holt's Hotel in the 
city of New- York, penetrated through 126 feet of 
stratified sands, blue clay, and river mud, when he 
came to the gneiss rock which underlies the whole 
island ; l^e then bored this rock 500 feet, the upper 
200 with an auger 3 inches in diameter, and the re- 
mainder with two and a half inch. He also pene- j 
trated the earth at the corner of Bleecker-street and | 
Broadway, with an auger 7 inches in diameter, to the i 
depth of 448 feet, 406 of which is in solid rock. 
This well furnishes 120,000 gallons of excellent 
water in ^4 hours ; and the water rises within 20 
feet of the surface. Where the hole is made into 
the earth, in order to prevent the sides from falling 
in, as well a^ the pscapo of the w^ter into the adjar 
