depth of 3 or 4 ft., under the stones on the beaches; they remain quiet by day, becoming active about twilight; the eggs are 1⅛ by ¾ in., white, with minute dull red dots at the larger end. According to Brünnich, this bird becomes so fat that the inhabitants of the Faroe islands string it to a wick, and use it as a lamp. Other species of this genus are found in America.—In the genus pelecanoides (Lacép.) the bill is shorter than the head, broad, depressed, and swelled at the sides; beneath the bill is a membranous pouch capable of extension; nostrils opening by two tubular apertures; wings very short, as are the tarsi and tail; toes long, the hind one wanting. A few species are described, inhabiting the coasts of New Zealand, Australia, and the extreme parts of South America; they are seen in troops, and dive very frequently, probably in search of small fish; they are rather poor fliers, compared with other petrels.—In the genus prion (Lacép.) the bill is longer, depressed, with nearly straight culmen, sides dilated near the base and beset posteriorly with fine parallel laminæ; nostrils with two openings, short and elevated; the hind toe a mere claw. The broad-billed petrel (P. vittatus, Lacép.), found between lat. 35° and 70° S., is bluish ash above, with tips of quills and wing coverts black; some of the characters of the bill resemble those of the fishing ducks. It is wild and solitary, a rapid flier, and constantly on the wing; the nests are made in society, in burrows about a yard deep, excavated in the sides of hills near the sea; the eggs are white, elongated, like those of a pigeon.—For the genus puffinus (Briss.) see Shearwater.
PETRIE, George, an Irish archæologist, born in Dublin in 1789, died Jan. 18, 1866. He studied painting in Dublin, and won a silver medal at the age of 14. He exhibited his first pictures at Somerset house, London, in 1816, and furnished many illustrations of Ireland for engravers. In 1832 he became associate editor of the “Dublin Penny Journal,” and in 1842 editor of the “Irish Penny Journal,” both illustrated. He was commissioned by the royal Irish academy to purchase rare manuscripts, and secured an autograph copy of the second part of the “Annals of the Four Masters,” and in 1831 published “Remarks on the History and Authenticity of the Autograph Originals of the Annals of the Four Masters.” In 1832 he received a prize of £50 and the gold medal of the academy for an essay on the round towers, enlarged and published under the title of “The Ecclesiastical Architecture of Ireland anterior to the Anglo-Norman Invasion” (Dublin, 1845). In 1836 he received the gold medal for his “Ancient Military Architecture of Ireland,” and in 1837 the old medal for his “History and Antiquities of Tara Hill.” He was the head of the historical and antiquarian department of the “Ordnance Memoir,” designed to accompany the survey, and collected more than 400 volumes of letters and documents. The first volume was published in 1839, but the work was never completed. He took down from the peasant musicians and singers much old and unwritten music, and published it in 1855. He wrote “Picturesque Sketches in Ireland” and “Views in the North of Ireland,” and contributed to the 18th volume of the transactions of the royal Irish academy an “Account of an Irish Reliquary called the Domnach Airgid” (1832), and “Remarks on the Book of MacFirbis” (1837). He was secretary and afterward president of the royal Irish academy, and received a pension of £300.—See “Life and Labors of George Petrie,” by W. Stokes (1868).
PETRIFACTIONS. See Palæontology.
PETROBRUSSIANS. See Bruys, Peter de.
PETROLEUM (Lat. petra, a rock, and oleum, oil), rock oil, a natural product of certain geological formations, sometimes rising to the surface through natural channels, forming springs, but chiefly obtained by boring. It was known to the ancient Greeks and Romans, and by Pliny, Tacitus, Vitruvius, and other Roman writers was designated bitumen, a word derived from the Greek πίττα, πίσσα, pitch, and probably first written pitumen. Among the localities cited where the liquid bitumen was found is Zacynthus (now Zante), one of the Ionian islands. As it is referred to by Herodotus, this spring must have been flowing more than 2,000 years. At Agrigentum in Sicily the petroleum was collected and burned in lamps. (Dioscorides, i. 99.) It was but little noticed during the middle ages, excepting in certain localities where it occurs in large quantities; but in modern times it has become one of the most important of natural productions. It occurs in rocks or deposits of nearly all geological ages, from the lower Silurian to the tertiary epoch. It is associated most abundantly with argillaceous shales and sandstones, but is found also permeating limestones, giving them a bituminous odor; and from these it often exudes, floating upon the streams and lakes of the region, or rising in springs. It often exists in subterranean cavities, situated along gentle anticlinals in the barren rocks of the region, the oil having collected in them from the subjacent strata, and having been retained by the impervious overlying sandstones. If the oil existed already formed, a slight elevation of temperature or hydrostatic pressure would force it into these cavities or bring it to the surface; but if it was formed by destructive distillation from materials within the rocks, considerable heat would be necessary.—Petroleum is very widely distributed, yet there are a few localities especially noted for its occurrence, among which are the following: Amiano and other places in the north of Italy, which have furnished the supplies used for lighting the cities of Parma and Genoa; Baku on the borders of the Caspian; the slopes of the Caucasus; Rangoon in Burmah; the island of Trinidad; and portions of the province of Ontario, Pennsylvania, Ohio, New York, West Virginia, and
