146 
GEOLOGY OF THE FIRST DISTRICT. 
but they break out at some distance from the shore, in consequence of the land declining 
almost insensibly from the hills. The great plain of Long island extends from the base of the 
hills south to the ocean, descending but a few feet to a mile. On Hempstead plains the wells 
are dug from sixty to one hundred and twenty feet deep, through beds of gravel and sand, be¬ 
fore water is reached, which is a little above the level of the ocean. The wells gradually de¬ 
crease in depth thence to the shore. On most of the farms in the interior, artificial means are 
are resorted to, to procure a supply of water for cattle and other farm stock. A basin-shaped 
excavation is made in the soil, and puddled with clay, and into this the surface waters are 
conducted during rains. They are called watering holes, and are a striking feature of the 
farming economy of the island. 
Good fresh water is often obtained on the shore, and on the beaches and spits, by digging 
down to the level of the adjacent salt water. This fact was communicated to me first by W. 
H. Sidell, a civil engineer, who had often thus quenched his thirst when surveying the shores 
and the long sand-spit near Oyster-pond point. This fact should be generally known. Its 
explanation is obvious. The rain, as it falls, sinks in the sand down to the water level, 
where it remains. As the tide rises, it rises and falls with it; and as the difference of spe¬ 
cific gravity is slight, it will not escape, unless the tide overflow the sand-bar or spit, and in 
this case it mixes with the salt water. 
Good fresh water may generally be expected to be found on beaches, spits and bars, where 
they are not overflowed by the tide, at the sea level. 
Water is found generally in abundance in penetrating the clay beds down to, or through 
the subjacent drift deposits, before reaching the rock, in the quaternary of the Hudson valley. 
This is observed as a general fact in digging and boring wells; and frequently the water 
flows from the surface of the earth, where the boring is through the clay beds, and the sur¬ 
face of the country at no great distance is higher. This is due to there being a head of 
water in the gravel beds ; and the clay beds being impervious, the water can not rise until an 
opening is made through the clay. The water will then rise, and if restrained by a tube, 
will rise to the level of its source, or overflow on the surface. Artesian wells are bored 
through various strata, where water is prevented from rising by their being impervious. Mr. 
Disbrow has bored a great number of wells, and many of them have overflowed at the sur¬ 
face. The salt marshes of Long island, and the adjacent islands of our coast, may probably 
have an abundance of good water by boring and tubing the wells. The water will either 
overflow, or rise to near the surface ; but if the sand and gravel beds communicate with the 
ocean, or with the salt water, the wells may be expected, after a long time, to yield brackish 
or salt water. Borings have often been made for artesian wells, in situations where the geo¬ 
logical structure was such that they could not be expected to be successful. New-York 
island is a good example. The strata there are vertical, or dip at a high angle, so that no 
water could be expected, except that flowing through the gravel beds in the depressions along 
the edges of the strata, parallel to the line of bearing. As the island is surrounded, at no 
great distance from every part of it, by deep channels, and as no portion is much elevated, and 
