LONG-ISLAND DIVISION. 
271 
The springs at the head and on the east side of Hempstead harbor, southwest of Oyster- 
bay harbor, head and east side of Cow bay, head of Coldspring harbor, Glen cove. Centre- 
port, Northport, Setauket harbor, and many others that might be designated, are dammed 
up, either by running a dam across the ravine, or along the edge of the bank where they 
break out. Ponds are thus formed that have no apparent source of supply, but which drive 
mills more or less constantly. They are of very great importance, as yielding a source of 
motive power, where the population would otherwise be dependent on steam or animal power 
to drive machinery, which are expensive; or be dependent on windmills which cannot be 
relied on, permanently, or even at regular penods of time. 
The reader, by referring to the map of Long island (vide Plate 1), will observe that the 
localities of nearly all these groups of copious springs are either at the heads of the bays and 
reenterings of the coast, or in the valleys prolonged beyond the heads of the bays, or at the 
heads of the small bays and marshes branching from the main bays. If the stratum of clay, 
that is generally the water-bearing stratum, be supposed perfectly horizontal, the flow of water 
would necessarily be greater in the situations indicated, than on the coast generally, or on the 
lateral shores of the bays; but we know the strata are more or less undulating, and it is 
believed that the evidences observed are sufiicient to indicate depressions of the water-bearing 
and other strata in the valleys of the reentering of the north coast. 
Valleys of Long Island. 
The general topographical features of Long island have already been indicated in a general 
way, the main features of which are, a range of hills extending from the western to the eastern 
extremity of the island, and occupying most of the northern half; and a nearly level plain, 
slightly undulating, with a very small declivity, extending from the southern base of the hills 
to the south shore. The careful observer will also have noticed, that there are valleys through 
the hills, from the heads of nearly all the bays on the north coast, which also extend south¬ 
wards across the south plain to the south shore. The surveys for the Long island railroad 
have shown that no location can be selected so as to avoid crossing these valleys ; but in all 
cases it has been necessary to construct embankments across them, to obtain a level grade 
for the road. They have the appearance of channels through which the water has flowed in 
tidal or other currents, before the emergence of the land from the ocean, and have either been 
excavated since the deposition of the strata, or else the currents setting through these chan¬ 
nels prevented the deposition of as much earthy matter as in other adjacent parts. The 
evidence preponderates in favor of the latter supposition, and that the same general cause has 
acted during the deposition of the various strata, from the lowest of these depositions that 
have come under observation, through the drift and quaternary periods, until the island emerged 
from the waters of the ocean, so that currents no longer flow across it. This shows an 
obvious reason wTip such quantities of spring waters flow from particular localities. On the 
south shore of the island, the same cause does not act. There the quaternary strata are all 
