THE DISTRIBUTION OF PETROLEUM.
We shall say but a few words on this subject, since its distribution within the Great Basin has been pretty thoroughly discussed in the preceding pages, while its existence in volcanic regions has also been mentioned. Its general distribution through all form ations and in all quarters of the earth is generally known. We will only call atten tion to a few localities where oil is found in conditions differing materially from those described.
The petroleum of Canada does not differ from that of Pennsylvania, though geologists assign it to the Corniferous limestone or the third oil-formation : on this subject, how ever, there is some disagreement, since others place it in the second formation, and on the same geological horizon with that of Venango. We have not given the subject much attention, and will not attempt to decide in which formation it is found. But whether its geological horizon be higher or lower, it cannot alter the fact of its existence in the same form and in the same circumstance and conditions as found in Venango county, Pennsylvania.
If it exists in the lower Devonian or upper Silurian, the rocks containing it come near to the surface where the Canadian petroleum is found, and, though the same forma tion may be over 2000 feet deep under Oil Creek, it is only from 300 to 500 where found in Chatham county, near Lake St. Clair, in Canada. At the greater depth under Oil Creek it would exist as gas only, but at the Canadian wells it would naturally be condensed as oil, from the escape of the hydrogen.
The oils of California and all or most of the great region west of the Rocky Moun tains are principally, if not entirely, of volcanic origin, and exist in the vicinity of volcanic regions. The many scattered deposits of coal of a later date than the true Carboniferous prove the fact of their volcanic origin, since they are found in almost every lithological formation. Like the eastern coal-fields of Massachusetts, Virginia, and North Carolina, they were only created when the temperature of the great volcanic ranges in which they are located admitted of the condensation of the gases, which naturally must have been of much later date than in the comparatively temperate regions at a distance in the waters of the Great Basin.
We cannot refrain from noticing the fact again in this connection, to call the attention of the thinking reader to the uniformity and beauty of every coincident, when we refeti the production of coal indirectly to the vapors of carbon, and directly to the resulting petroleum and bitumen.
We need not state that vapor or gases enshrouded the earth when a thousand volcanoes vented their streams of molten lava into the waters that filled its deep places ; nor need it be argued that the vapor of carbon and the hydrogen of water should unite under the heat produced, forming carburetted hydrogen gas.
This could not result in oil under the heat that existed in the vicinity of volcanic action ; but at a distance, where the molten lava, shivered by its contact with water, precipitated as sediment in the waters of the wide Appalachian basin, the temperature would be much reduced, and the carbon would part with much of its hydrogen, and become in consequence petroleum.
In every great coal-field known, a process similar to this took place. In the Welsh an thracite field it was almost identical, and in the Great Northern coal-field of Northum berland and Durham in Englaiid, while the manner of its production might have been quite different, the principle was the same. There the oil forming coal might not be derived from distant sources of heat, but the great dikes penetrating the coal-field might have produced the vapor and gas of the hydro-carbons. These dikes are of all ages. The " whin-sill" underlies the coal, while the great ninety fathom dike reaches the sur face. At some points the coal has been formed on the dikes, and of course subsequent to their formation ; while at others the trap invades the coal measures from bottom to top.