[008] See Humboldt's Personal Narrative, vol. v. p. 46. Also St. Pierre's Paul and Virginia.--JAMES.
[009] The great coal field of which that of western Pennsylvania is a part, is eight hundred miles in length and one hundred and eighty in width. Besides Pennsylvania, it includes southeastern Ohio, the western part of Maryland, most of West Virginia, portions of Kentucky and Tennessee, and the northern end of Alabama. In Pennsylvania, the main field does not extend farther north than a central east-and-west line, but several great projections reach almost to the northern boundary. East of the Alleghenies the deposits are anthracite, while the bituminous fields occupy the southwestern section of the state.--ED.
[010] The uses of petroleum have been known from time immemorial; but the quantities laboriously gathered from springs like those here described were economically insignificant. The importance of the industry dates from the discovery, in 1858, that vast quantities of oil could be obtained by drilling wells. The excitement which ensued was comparable to that caused by finding gold in California. Among United States exports, petroleum products now rank near the top of the column.--ED.
[011] James implies that the Onondaga salt deposits are in the Carboniferous system. Such deposits, however, occur in almost every geological system, from Silurian to Recent, and the New York areas are found in the Silurian; the Kanawha salt district is Carboniferous. The Onondaga springs were known to Jesuit missionaries as early as 1646, and soon after were utilized in making salt for the Indian trade. The existence of salt licks and springs west of the mountains was an important factor in the settlement of the trans-Allegheny country. The pioneers could not have ventured so far from the coast without a native supply of this necessity.--ED.
[012] So-called gas springs were known to settlers long before any attempt was made to utilize the product; about 1821, burners were first devised by which it was made to serve for lighting purposes. For several years after the beginning of the oil industry, gas was generally considered as a worthless and troublesome by-product, and not many wells were drilled for it until after 1870. The pressure of the gas is sometimes enormous--as much as three hundred and fifty pounds to the square inch has been noted. Natural gas consists essentially of carburetted hydrogen.--ED.