Page:EB1911 - Volume 21.djvu/71

Rh to the area occupied by the parent rock (e.g. the granite), or to its immediate vicinity, and within the zone which has been greatly heated by the plutonic intrusion, viz. the contact aureole. Another very important factor in producing the coarse crystallization of the pegmatite veins is the presence of abundant water vapour and other gases which served as mineralizing agents and facilitated the building together of the rock molecules in large crystalline individuals.

Proof that these vapours were important agents in the formation of pegmatites is afforded by many of the minerals contained in the veins. Boron, fluorine, hydrogen, chlorine and other volatile substances are essential components of some of these minerals. Thus tourmaline, which contains boron and fluorine, may be common in the pegmatites but rare in the granite itself. Fluorine or chlorine are present in apatite, another frequent ingredient of granite pegmatites. Muscovite and gilbertite both contain hydrogen and fluorine; topaz is rich in fluorine also and all of these are abundant in some pegmatites. The stimulating effect which volatile substances exert on crystallizing molten masses is well known to experimental geologists who, by mixing tungstates and fluorides with fused powders, have been able to produce artificial minerals which they could not otherwise obtain. Most pegmatites are truly igneous rocks so far as their composition goes, but in their structure they show relations to the aqueous niineral veins. Many of them for example have a comby structure, that is to say, their minerals are columnar and stand perpendicular to the ualls of the fissure occupied by the vein. Sometimes they have a banding owing to successive deposits having been laid down of different character, mica may be external, then feldspar, and in the centre a leader or string of pure quartz. In pegmatite veins also there are very frequently cavities or vugs, which are lined by crystals with very perfect faces. These bear much resemblance to the miarolitic or drusy cavities common in granite, and like them were probably filled with the residual liquid which was left over after the mineral substances were deposited in crystals.

Pegmatites are very irregular not only in distribution, width and persistence, but also in composition. The relative abundance of the constituent minerals may differ rapidly and much from point to point. Sometimes they are rich in mica, in enormous crystals for which the rock is mined or quarried (India). Other pegmatites are nearly pure feldspar, while others are locally (especially near their terminations) very full of quartz. They may in fact pass into quartz veins (alas kites) some of which are auriferous (N. America). Quartz veins of another type are very largely developed, especially in regions of slate and phyllite, they are produced by segregation of dissolved silica from the country rock and its concentration into cracks produced by stretching of the rock masses during folding In these segregation veins, especially when the beds are of feldspathic nature, crystals of albite and orthoclase may appear, in large or small quantity. In this way a second type of pegmatite (segregation pegmatite) is formed which is very difficult to distinguish from true igneous veins. These two have, however, much in common as regards the conditions under which they were formed. Great pressures, presence of in water, and a high though not necessarily very high temperature were the principal agencies at work.

 PEGNITZ, a river of Germany. It rises near Lindenhard in Upper Franconia (Bavaria) from two sources. At first it is called the Fichtenohe, but at Buchau it takes the name of the Pegnitz, and flowing in a south-westerly direction disappears below the small town of Pegnitz in a mountain cavern. It emerges through three orifices, enters Middle Franconia, and after flowing through the heart of the city of Nuremberg falls into the Regnitz at Furth.

The Pegnitz Order (Order of the society of Pegnitz shepherds), also known as “the crowned flower order on the Pegnitz,” was one of the societies founded in Germany in the course of the 17th century for the purification and improvement of the German language, especially in the domain of poetry. Georg Philipp Harsdörffer and Johann Klaj instituted the order in Nuremberg in 1644, and named it after the river. Its emblem was the passion flower with Pan's pipes, and the motto Mit Nutzen erfreulich, or Alle zu einem Ton einstimmig. The members set themselves the task of counteracting the pedantry of another school of poetry by imagination and gaiety, but lacking imagination and broad views they took refuge in allegorical subjects and puerile trifling. The result was to debase rather than to raise the standard of poetic art in Germany. At first the meetings of the order were held in private grounds, but in 1681 they were transferred to a forest near Kraftshof or Naunhof. In 1794 the order was reorganized, and it now exists merely as a literary society.

 PEGOLOTTI, FRANCESCO BALDUCCI (fl. 1315-1340), Florentine merchant and writer, was a factor in the service of the mercantile house of the Bardi, and in this capacity we find him at Antwerp from 1315 (or earlier) to 1317; in London in 1317 and apparently for some time after; in Cyprus from 1324 to 1327, and again (or perhaps in unbroken continuation of his former residence) in 1335. In this last year he obtained from the king of Little Armenia (i.e. medieval Cilicia, &c.) a grant of privileges for Florentine trade. Between 1335 and 1343, probably in 1339–1340, he compiled his Libro di divisamenti di paesi e di misuri di mercatanzie e d'altre cose bisognevoli di sapere a' mercatanti, commonly known as the Pratica della mercatura (the name given it by Pagnini). Beginning with a sort of glossary of foreign terms then in use for all kinds of taxes or payments on merchandise as well as for “every kind of place where goods might be bought or sold in cities,” the Pratica next describes some of the chief trade routes of the 14th century, and many of the principal markets then known to Italian merchants; the imports and exports of various important commercial regions; the business customs prevalent in each of those regions, and the comparative value of the leading moneys, weights and measures. The most distant and extensive trade routes described by Pegolotti are: (1) that from Tana or Azov to Peking via Astrakhan, Khiva, Otrar, Kulja and Kanchow (Gittarchan, Organci, Ottrarre, Armalecco and Camexu in the Pratica); (2) that from Lajazzo on the Cilician coast to Tabriz in north Persia via Sivas, Erzingan and Erzerum (Salvastro, Arzinga and Arzerone); (3) that from Trebizond to Tabriz. Among the markets enumerated are: Tana, Constantinople, Alexandria, Damietta, and the ports of Cyprus and the Crimea. Pegolotti's notices of ports on the north of the Black Sea are very valuable, his works show us that Florentine exports had now gained a high reputation in the Levant. In other chapters an account is given of 14th-century methods of packing goods (ch. 29); of assaying gold and silver (ch. 35); of shipment; of “London in England in itself” (ch 62); of monasteries in Scotland and England (“Scotland of England,” Scozia di Inghilterra) that were rich in wool (ch. 63). Among the latter are Newbattle, Balmerino, Cupar, Dunfermline, Dundrennan, Glenluce, Coldingham, Kelso, Newminster near Morpeth, Furness, Fountains, Kirkstall, Kirstead, Swineshead, Sawley