"Beginning with the uppermost, the rocks of Saratoga county are:

1. The Hudson river and Utica shales and slates.

2. The Trenton limestone.

3. The calciferous sand rock, which is a silicious limestone.

4. The Potsdam sand stone; and

5. The Laurentian formation of gneiss and granite, of unknown thickness.

"The northern half of the county is occupied by the elevated ranges of Laurentian rocks; flanking these occur the Potsdam, Calciferous and Trenton beds, which appear in succession in parallel bands through the central part of the county. These are covered in the southern half of the county by the Utica and Hudson river slates and shales.

"The most remarkable feature is, however, the break, or vertical fissure, which occurs in the Saratoga valley, which you see indicated in the cut. Notice, especially, the fact that the strata on one side of the fissure have been elevated above their original position, so that the Potsdam sandstone on the left meets the edges of the calciferous sand rock, and even the Trenton limestone on the right. It is in the line of this fissure, or fault, in the towns of Saratoga and Ballston that the springs occur.

"The Laurentian rocks, consisting of highly crystalline gneiss, granite and syenite, are almost impervious, while the overlying Potsdam sandstone is very porous, and capable of holding large quantities of water. In this rock the mineral springs of Saratoga probably have their origin. The surface waters of the Laurentian hills, flowing down over the exposed edges of the Potsdam beds, penetrate the porous sandstones, become saturated with mineral matter, partly derived, perhaps, from the limestones above, and are forced to the surface at a lower level, by hydrostatic pressure. The valley in which the springs all occur indicates the line of a fault or fracture in the rocky crust, the strata on the west side of which are hundreds of feet above the corresponding strata on the east.

"The mineral waters probably underlie the southern half of the entire county, many hundred feet below the surface; the accident of the fault determining their appearance as springs in the valley of Saratoga Springs, where, by virtue of the greater elevation of their distant source, they reach the surface through crevices in the rocks produced by the fracture.

"It is probable that water can be obtained anywhere in the southern portion of the county by tapping the underlying Potsdam sandstone. In these wells the water usually rises to and above the surface. Down in the rocky reservoir the water is charged with gases under great pressure. As the water is forced to the surface, the pressure diminishes, and a portion of gas escapes with effervescence. The spouting wells deliver, therefore, enormous volumes of gas with the water, a perfect suds of water, carbonic acid and carburetted hydrogen.

"The common origin of the springs is shown by the analysis: all contain the same constituents in essentially the same order of abundance; they differ in the degree of concentration merely. Those from the deepest strata are the most concentrated. The constituents to which the taste of the water and its most immediate medicinal effects are due, are: Chloride of sodium, bicarbonate of lime, bicarbonate of magnesia, bicarbonate of soda and free carbonic acid. Other important, though less speedily active, constituents are: Bicarbonate of iron, bicarbonate of lithia, iodide of sodium and bromide of sodium."