The oil region of Venango County, as far as has been explored, is confined to the creek and river bottoms. In connection with wells that have been opened, there is a superincumbent stratum of earth, varying from ten to sixty feet in thickness: underlying this is a stratum of argillaceous shale, generally about one hundred and eighty feet in thickness, and then a stratum of white sandstone. Sometimes this sandstone is intermingled with red, presenting a ruddy appearance as the sand is withdrawn from the well in the process of boring. Occasionally in passing through the shale, small fissures in the rock are passed through, with circumstances indicating the presence of a stratum or vein of water, as at such times the sand accumulated in boring all disappears, leaving the bits clean and bright. At other times small veins or cavities of petroleum are pierced, the product of which rises to the surface of the well, and indicates its presence by appearing in the sand pump. In the earlier stages of the business this 'show of oil,' as it was termed, was considered most favorable to ultimate success; but latterly it is not regarded as essential, as many first-class wells have been discovered without the intermediate show; and on the other hand, there has been many a brilliant show that has resulted in failure and disappointment. The presence of surface oil is not always a sure criterion in deciding upon a location for a well. Oftentimes very fine wells are opened in localities where no oil has been found on the surface, and no appearance of oil having been obtained at any previous time in the neighborhood. Perhaps the most unsuccessful operations in the whole Oil Creek valley have been in the midst of the ancient pits that have already been alluded to. Wells have been bored in the bottom of these pits without the least success. At a point near the bank of the Alleghany, some two miles above Franklin, there was a well-known oil spring some forty years ago. It supplied the family that lived near it as well as the surrounding neighborhood with petroleum for medical and other domestic purposes to the extent of their wants. For many years the supply has entirely failed. During a recent excavation, at the precise spot where it was known formerly to exist, for the purpose of laying the abutment of a bridge, no trace of oil was found--not even a discoloration of the earth.