As to the abundance of the supply in this region, there can be but little doubt. Wells seem at times to become exhausted, but it is from local causes. At times a cavity may be tapped that has been supplied from a very small avenue, and may be readily exhausted, but exhausted only to be refilled again. The fact that wells do not interfere with each other, even when but fifty feet apart, is evidence that the supply is not confined to a limited stratum, but is drawn from the great deeps beneath. The existence of the ancient oil pits, before alluded to, assures us that the supply has been continued for centuries; and observation confirms this, as we have noticed the hitherto unused treasure bubbling up silently through the crevices in the rocks and gradually evaporating amid the sands, or arising in the beds of the streams and floating down upon their surface. The history of the petroleum trade in other lands encourages us as to the abundance of the supply in our own. In the northern part of Italy, petroleum has been collected for more than two hundred years, without any intimation that the supply is being exhausted. In Burmah a supply has been drawn from the earth for an unknown period, and so far are these wells from exhaustion that they yield at the present time over twenty-five millions of gallons per annum. We may well suppose, then, that the treasure brought to light in such abundance in our day will not be readily exhausted--that as the coals are found in illimitable abundance for fuel as the forests fail, petroleum for illuminating purposes will be found in like profusion. We have said that the petroleum trade has known no infancy, but has sprung at once into maturity. The oil wells of Venango County alone produced, during the first year of their operation, more oil than the entire product of the whale fisheries during the most favorable and prosperous year in their history. At the present time, after a lapse of little more than two years, the daily product of the wells on Oil Creek alone is computed to be over six thousand barrels. And in this neighborhood the quantity might be wellnigh doubled, were it not for the low price the product commands. Petroleum differs in its characteristics in different localities. It is usually heavier in the shallow wells than in those that are deeper. Ordinarily it is of a greenish hue, that changes to a reddish as the oil becomes lighter and more evaporative. It is all characterized by a strong and pungent odor peculiar to itself. The gravity of the various kinds of oil is ascertained by the oleometer. The lighter oils are found on Oil Creek, and are about 40 deg. to 46 deg. Baume; at Franklin, from 30 deg. to 32 deg..