The coal formation, containing the beds which have long been wrought near Pittsburgh, appears to be of great extent; but we are unable particularly to point out its limits towards the north and east.[009] One hundred miles above Pittsburgh, near the Alleghany river, is a spring, on the surface of {14} whose waters are found such quantities of a bituminous oil, that a person may gather several gallons in a day. This spring is most probably connected with coal strata, as are numerous similar ones in Ohio, Kentucky, &c.[010] Indeed, it appears reasonable to believe that the coal strata are continued along the western slope of the Alleghanies with little interruption, at least as far northward as the brine springs of Onondago. Of all the saline springs belonging to this formation, and whose waters are used for the manufacture of salt, the most important are those of the Kenhawa, a river of Virginia. Others occur in that country of ancient monuments, about Paint Creek, between the Sciota and the Muskinghum, near the Silver Creek hills in Illinois; and indeed in almost all the country contiguous to the Ohio river. Wherever we have had the opportunity of observing these brine springs, we have usually found them in connexion with an argillaceous sandstone, bearing impressions of phytolytes, culmaria, and those tessellated zoophytes, so common about many coal beds.[011] It appeared to us worthy of remark, that in many places, where explorations have been made for salt water, and where perpendicular shafts have been carried to the depth of from two to four hundred feet, the water, when found, rises with sufficient force to elevate itself several feet above the surface of the earth. This effect appears to be produced by the pressure of an aërial fluid, existing in connexion with the water, in those cavities beneath the strata of sandstone, where the latter is confined, or escaping from combination with it, as soon as the requisite enlargement is given, by perforating the superincumbent strata. We have had no opportunity of examining attentively the gaseous substances which escape from the brine pits, but from their sensible properties we are induced to suppose, that carbonic acid, and carburetted hydrogen, are among those of most frequent occurrence.[012]