"The mountains rise above us, but who can write an indisputable history of the precise manner of their construction? The oil sands spread out beneath our feet; who can go. down into the dark places of the deep, or back into the unknown ages of the abysmal past, and gather the facts for a special and detailed account of their deposition, which shall carry the conviction of truthfulness to all who may read it? The manner in which these oil sands were deposited is one of these measurably uncertain problems. Many strange and fanciful theories have been advanced to account for their presence in the position where they have been found. They have been supposed by some to have been ejected through a portion of the superstrata by subterranean force operating beneath them. They have been described, and by reputable geologists. too, on the one hand, as fractured anticlinal arches, on the other, as synclinal troughs traversed by fissures and crevices containing salt-water, oil, and gas. They have been pictured as long sand-cores, cast in grooves a few yards wide and running as straight as an arrow for miles, as if some huge grooving-machine had passed over the bed rocks of shale in a northeast-southwest direction, making an uniform furrow a few rods wide and thirty feet or more in depth in the centre, which was, in some unaccountable manner, filled in at a later day with coarse sand and gravel." Mr. Carll does not stop to refute these baseless theories and speculations, but proceeds to examine, "1st, what dynamical agents were employed in the construction or building up of these rocks; 2d, what was the

character of the materials used in the formative process; and 3d, with such forces and such materials what would be the probable structure of the rocks, judging from what we see under analogous circumstances at the present time?"

The space which we have appropriated to this branch of our subject will not permit us to present his views regarding this formation, but that these sand rocks are of sedimentary origin seems to us beyond dispute. Sedimentary rocks are defined by the geologist Lyell to be those which are formed from materials thrown down from a state of suspension or solution in water." The materials comprising these may vary greatly in relative coarseness or fineness. In one position, boulders, such as "pavingstones," may may have been hurled by the violence of a rushing current and deposited in one place; stones of a smaller size are carried further, and find a resting place quite beyond the limit of the former; while gravel and sand of varying fineness are carried still further, and deposited at a distance from the others, exactly proportionate to the size and weight of the particles composing the drift. The conclusion, then, is irresistible, if these sand strata are sedimentary they could only have been placed in their present positions by currents of oceans, lakes, or rivers. There appears to be no other force now in operation on the face of the earth, except the eroding and buoyant forces of water in rapid motion, sufficient to explain the observed phenomena. The materials composing the different sand rocks are laid bare by the operations of the "drill," and also by the inspec

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tion of the outcropping layers of the same deposit in some contiguous section. They vary from coarse conglomerates, containing quartz pebbles, occasionally two inches in diameter, through all grades of conglomerates, down to pebble sand, sandstone, sandy shale, slate, and the most finely levigated mud rock or soap-stone,' of the driller." The great irregularity and apparent disorder noticed in the distribution of these patches of sand rock may thus be accounted for when we take in connection with this the fact that these forces are varying continually in energy, "affected by winds and tides and storms, affected by changes of levels intensifying their powers at one time in this place, at another time in that. The oil sands are frequently massive conglomerates, made up of the coarsest materials to be found in the formation to which they belong. The conclusion is unavoidable, therefore, that they owe their origin to the action of the strongest depositing currents prevailing at the period of their deposition." It is also a reasonable deduction, that these deposits were made near the coast line, and were subsequently submerged by the subsidence of the land over which the ocean rolled. That there were many alternations of the level of the ocean and the land, occasioned by the subsidence just alluded to, or by the uprising of mountain ranges, is a fact too plainly written on the stone leaves of the "book of Nature" to be questioned, As we come to turn over these leaves we find that Nature has there recorded also-the day's work.

These oil sands, lying within the district before men

tioned, have been accurately mapped out, and their relative distances from the surface carefully measured. They appear to have a well-defined relation to certain wellknown geological formations, cropping out in certain locations. Mr. Carll states: "The relative geological position of the several oil-bearing horizons may be ascertained approximately by measuring down from the base of the bottom member of the carboniferous series. The Olean conglomerate, a persistent and well-defined stratum, seen on the high places in all these districts, is a convenient and reliable datum to calculate from. Starting, therefore, at the Olean conglomerate, at the depth of 450 feet, we have the first sandstone, unproductive here; at the depth of 800 feet we have the Venango group of oil sand; between this and N. Warren oil horizon, at the depth of 1100 feet, we have unproductive shales; at 1300 feet we have the Warren third sandstone; at 1450 feet we have the Clarendon third sandstone; at about the same depth we have the Bradford slush oil; at 1625 feet we have the Cherry Grove third sandstone; at 1850 feet we have the Cooper or Forrest Company third sandstone; at about the same depth we have the prolific third sandstone of the Bradford district; and at the depth of 1900 feet we have the Allegheny sand rock." At the present time the Bradford district is producing most of the oil found within the limits of this belt. It has been estimated that there are now about twelve thousand producing wells within an area of one hundred and fifty square miles. The productive spots have been pretty well defined by the line of

"dry holes" which surround them. It is entirely beyond the skill of even the professional geologist to define, in a certain district, the area of these producing sands, with the data before him, to which we have before adverted. Taking into consideration the dip of the strata, he can tell accurately the depth to which the drill must go to pierce the oil horizon, but to foretell that the particular formation he is in search of will be found in that particular locality, is beyond his ability; and if it is not there, what has caused its removal is equally beyond his knowledge. These productive spots evidently belong to the same horizon, and are geologically of the same age. They appear to have been formed under precisely the same conditions, and yet they have no connection whatever with each other, and between them, at times, there are miles of unproductive territory. A great deal of capital and labor are vainly spent in prospecting for oil by those who ignore the intelligent deductions of science in a matter of this kind. Many, in their blind search for oil, insist that these sand strata must necessarily be continuous, because the geologist cannot exactly define the reason why they are not so. In a contest of opinion the drill must decide. There are those again who "ignore all consideration of age of rocks on stratigraphy, and make no distinction between the oilproducing sand belonging to the carboniferous formations at Dunkard's Creek and those of the Lower Chemung at Warren or Bradford."

The author is indebted, also, for some valuable matter in connection with these different sand rocks, to Mr. Charles