164 
HELDERGERG DIVISION. 
absorbed by the gravel, sand, clays, etc. which constitute the drift beds. However this 
may be, it seems more rational to suppose that deep excavations, forming basins, have 
been hollowed out of these rocks, into which the drift lias been precipitated. These drift 
beds are cpiite pervious, but they rest on an impervious foundation ; and the saline waters, 
which are supposed to be formed in the rock, flow out and accumulate in the beds of 
drift, which, when penetrated, give exit to them. This appears from the fact that when, 
on boring, the instruments soon penetrate into the drift, the workmen are encouraged to 
proceed, because experience has proved that in such a case a great flow of water is sure to 
be obtained. 
There is another fact worthy of notice, and which is important to the valley of Onondaga 
lake : it is this, that an impervious stratum of marl overlies nearly the whole region. This 
serves to keep the surface waters from .intermingling directly with the waters below, or, 
in other words, requires the water to penetrate from the distant slopes, and to traverse a 
large space in order to reach the basin of the lake, and thus to become highly charged 
with saline matter. This impervious stratum of marl overlies all the beds, inasmuch as it 
is the most recent. Whether it is now increasing in thickness, is not determined. Tufa 
is continually forming; and all the waters of this region, being charged with calcareous 
matter, must part with it whenever their flow is interrupted, and hence we see it gathering 
upon stones, sticks and leaves, and even in many cases petrifying them. 
The annexed diagram (fig. 28) is an imaginary section of the basin of Onondaga lake, 
and represents our view of the relations of the masses concerned in the origin of the Onon¬ 
daga salt springs. 
IFig. 2S. 
L. Onondaga lake, a, a, a. Impervious marl, b, b, b. Drift nearly filling the valley, e, c. Gypseous shales with 
hopper-form cavities, e, e. Red shale, d, d. Niagara limestone. 
The salt wells penetrate the drift to the depth of 340 - 350 feet, and quite large cobble¬ 
stones have been brought up from that depth. The strength of the water increases with 
the depth. The stones brought up, are derived from the harder parts of the Medina sand¬ 
stone. 
It is proper to remark, before closing, that it is not well settled whether the salt, the 
chloride of sodium, is merely a dissolved salt already formed and enclosed in the inter¬ 
stices of the rock, or is actually formed daily from elements contained in the rock, and 
