PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 877 



age. The hopper tapered to a wooden tube, twelve inches square 

 and twenty-nine feet long, which raised the water to the surface 

 of the ground, where it was terminated by a glass tube, three feet 

 high. The column of water above the rock is thus thirty-seven 

 feet high. The water flows over the rim of the glass tube, though 

 the pressure of the column of water reduces the quantity far 

 ])elow what escaped at the bottom of the excavation. The flow 

 of gas is a1)undant and constant; but every few minutes there is 

 a momentarj' evolution of an extraordinary quantity, which causes 

 the water in the tube to boil over the rim. 



The appearance of this fountain, on a bright sunny day, is most 

 beautiful ; the bubbles of carbonic acid gas, as they rise through 

 the water, appearing like struggling globules of mercury. 



Geology. 



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 sili- 

 cious limestone. 4. The Potsdam sandstone ; and 5. The Lauien- 

 tian formation 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 country. These are covered in the southern half of 

 the county by the Utica and Hudson river slates and shales. 



The Laurentian rocks, consisting of highly crystalline gneiss, 

 granite, and sj-enite, are abnost impervious, Avhile the overlying 

 Potsdam sandstone is very porous, and capable of holding lai-ge 

 quantities of water. In this rock the mineral springs of Saratoga 

 prol)ably 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 ar& 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 



