Whether the component materials or the great body of this oil exist in the sand rock where it is found, or at a depth beyond the present reach of the drill, is not a question of direct importance. What is being sought for is the location of the vent-holes by which this oil reaches within drilling distance of the surface of the earth, whether such vent-hole consists of an open sand rock or sponge as in Pennsylvania, or of an anticlinal or system of broken rocks es in W. Virginia. From the fact that coal and similar minerals are mined in continuous beds, stretching often over counties and states, it would be natural to suppose that the sand rocks cf the separate oil districts are connected in the same way. The extent of the beds of the upper sand rocks, near the surface of the earth, is so much greater than that of the oil-bearing rock, that the proposition is substantially true so far as they are concerned, with the exception that they are not found at a positively uniform horizon, but overlap and underlie each other at the edges.
A well drilled anywhere in the region will find a 1st sand ; and sometimes a 2nd, and invariably some "mountain sands," as they are called, are found even above these. Oil has been found in small quantities in the 1st and 2nd sand rocks, in detached spots, and from the earliest wells, but the bulk of the product has been obtained from the 3rd sand. From the means within reach at present for defining the position of this rock, there is every reason to believe that it is situated approximately throughout the region under consideration on the same geological horizon.
The productive ground in the Pennsylvania region is an area overlying, at 500-1500 ft., a bed of porous conglomerate, 3-75 ft. thick, the thickest part of the rock giving the best well, and this thickest part being generally found in the centre of the area, the rock tapering off at the edges.
When a well is drilled in an untried locality, and the 3rd sand rock is found of any thickness, whether with much or little oil, this well is followed by others situated in different directions from it, until the thickest part of the sand rock is discovered, and a good well is the result ; and it is not long before the edge, where the rock thins out, can be mapped on the surface of the ground above it. There is, therefore, within reach of the drill, no continuous bed of oil-bearing sand rock, but a series of scattered disc-shaped deposits. These separate and detached beds of 3rd sand rock are lens-shaped, being thin at the edges, as before stated.
The use of the term "oil-belt," has led to some misconception ; lines which were run across the surface of the country for many miles, in courses varying from N. 14° E. to N. 22° E., have been found to intersect the surfaoe directly over these producing beds of 3rd sand, but in separate places, and widely apart. The value of this discovery is doubtless confined to the extent of the conformity of these lines with the general course of the current which transported the material to form the deposit.
It would seem that all the oil rooks of the region, even if they be disconnected and scattered through the strata at irregular distances, lie at about the same general geological horizon.
The lowest sand rock as yet reported by any oil driller is in Jonathan Watson's deep well, which was drilled on the flat, in the City of Titusville, at a point 1195 ft. above sea-level, and in which a sand 20 ft. thick and containing some green oil, was said to have been passed through at a depth of 1976 ft. This sand was described as a white pebble conglomerate, similar in every respect to the ordinary 3rd sand. The next is the reported 3rd sand of Watson's well at a depth of 1507 ft. from the surface. The lowest 3rd sand of the oil-region proper is found at Tidioute, at a depth of 140 ft. below the first bench on the river, but not at a corresponding depth under the hills on either side. The sand rock there, if it be the same, is considerably higher ; but when penetrated, in the hopes of finding the river-sand, only "knocked the bottom out of the well." No small amount of oil has been produced from a 1st sand at Tidioute, found on the river at a depth of less than 100 ft. On the river-bank of the Economy tract, a well struck in a crevice at 99i ft., in 1861, produced oil steadily for 8 years ; and 4 other producing wells in the vicinity were not over 150 ft. in depth. From Enterprise and Titusville to Oil City, the 3rd sand, which is found at an average depth of 450 ft., follows nearly the fall of the water-shed, being found at Oil City at a depth of 475 ft., and along Oil Creek almost uniformly between these points. At Petroleum Centre, there appears to be a similar deviation ; also at Church Run, near Titusville. Surface oil has, likewise, been found in the 1st and 2nd sand rocks on Oil Creek. The Drake well found the sand at 71 ft., and produced for some time 25 barrels a day. Some wells at Miller farm also found oil for a short time at 225 ft., in what was probably a split 1st sand.