231 



PLECTOGNATHI 



PLEISTOCENE 



nation obtained by an appeal to universal suffrage. 

 Tim-, Louis Napoleon was chosen president, arid 

 subsequently emperor, by a plebiscite, and in 1870 

 obtained the sanction of still a third one I 7A million 

 votes). The word is borrowed from the Latin; 

 but the plebiscitttm of the Romans properly meant 

 only a law passed at the Comitia Tributa i.e. 

 assembly of the plebs, or 'commons,' as distin- 

 guished from the nobles. The word is often used 

 in Britain for an attempt to secure an expression 

 of opinion on some special point of local interest by 

 all the inhabitants of a district often by means of 

 return post-cards. 



PlertOtcnathi, an order of Bony Fishes (q.v.). 



Pledge. See PAWNBROKINO. 



Pleiades, in Greek Mythology, were, according 

 to the most general account, the seven daughters 

 of Atlas and Pleione, the daughter of Oceanus. 

 Their history is differently related by the Greek 

 mythologists : according to some authorities, they 

 committed suicide from grief, either at the death 

 of their sisters, the Uyades, or at the fate of their 

 father. Atlas (q.v.); according to others, they were 

 companions of Artemis ( Diana), and, Iteing pursued 

 by Orion (q.v.), were rescued from him by the gods 

 by being translated to the sky ; all authorities, 

 however, agree that after their death or translation 

 they were transformed into stars. Their names are 

 Electra, Maia, Taygete, Alcyone, Cela>no, Stero|>e 

 (the invisible one), and Merope. The group or 

 constellation of the Pleiades, called the 'Seven 

 Stars,' is placed on the shoulder of Taurus, the 

 second sign of the Zodiac, and form, with the pole- 

 star and the twin Castor and Pollux, the three 

 angular points of a figure which is nearly an 

 equilateral triangle. But, if looked at directly, 

 only six stars are visible to the eye, though, if the. 

 eye is turned sideways, more can be seen ; a good 

 telescope shows fifty or sixty in the area. The 



? holographic chart produced by M. M. Henry in 

 888 shows 2326 stars, with nebulie intermixed. 

 The name Pleiad is frequently applied to reunions 

 of poets in septenary groups ; and this use of the 

 word dates from the time of Ptolemy Philadelphia 

 at Alexandria, who treated seven Greek poets with 

 special distinction, and denominated them his 

 pleiatl. His example was followed by Charlemagne. 

 But the name Pleiade is sjiecially associated with a 

 group of 16th-century French writers, of whom 

 Ronsard (q.v.) and Du Bellay (q.v.) are the most 

 notable, who endeavoured with marked result to 

 reform the French language and literature after 

 classical models. The other names are Lazare de 

 Ba'if, ambassador at the diet of Spires ; Jean 

 Dorat, a celebrated Hellenist; Amadis Jamin ; 

 Etienne Jodelle; and Pontus de Thiard. In place 

 of the two last, other authorities give Scevole de 

 Saint Marthe and Marc Antoine Muret (q.v.); 

 and instead of Jamin, Belleau. 



Plcloeene. See PLIOCENR 



ririorhroism. In some crystals, such as 

 some specimens of topaz, three distinct colours 

 may be observed on looking through them along 

 three rectangu jar axes. In intermediate direction* 

 intermediate tints may be observed : and thi- pro- 

 perty is that of pleiochroism or polychroism. In 

 some other cases a similar range of intermediate 

 tints may be observed, lying between two extreme 

 tinl-< visible along two axes (dichroic crystals e,g. 

 iolite or sapphire <feau, and some specimens of 

 mica). 



PlelosaiiruH. See PLESIOSAURUS. 



PINslorene (Gr., 'most recent') or GLACIAL 

 Sv.sTKM. Thin system comprises the older accu- 

 mulations belonging to the Quaternary or Post- 

 Tertiary division. Almost all the molluscs met 



with in beds of this age are existing species. The 

 system is termed Pleistocene or Glacial according 

 as we have reference to the character of its organic 

 remains or to the physical conditions under which 

 the greater portion of its deposits were accumu- 

 lated. These deposit* are of very diverse nature 

 and origin, and are subject to endless modifica- 

 tions, but nevertheless they show certain well 

 marked phases which are persistent over \viilc 

 areas. Thus, throughout all northern Europe and 

 the hilly and mountainous districts of the central 

 and southern regions of the continent they exhibit 

 the same general character and succession. The 

 deposits of these regions consist for the most "part 

 of glacial and lluvio glacial detritus, which betoken 

 the former presence of a great ice-sheet in northern 

 Europe, and of extensive snowfields and glaciers 

 in the mountain districts farther south. For an 

 account of these deposits and glaciation generally, 

 see GLACIAL PERIOD. In the regions outside of 

 the glaciated areas the Pleistocene system is repre- 

 sented principally by fluviatile accumulations, cal- 

 careous tufas, r>eat, and deposits in caves. The old 

 river-gravels, &c. are well seen in the vallixs 

 of southern England, France, Belgium, central 

 Europe, Spain and Portugal, Italy, &c., where 

 they occur at the surface. Rut when they are 

 followed into regions in which glacial and liuvio- 

 glacial accumulations are well developed they dis- 

 appear underneath these or are dovetailed with 

 them. Cave-deposits are of course met with even 

 in glaciated regions, but in such countries no 

 Pleistocene accumulations overlie the glacial and 

 fluvio-glacial detritus of the latest cold stage of the 

 glacial period. 



Thus, in general terms, the Pleistocene deposits 

 of northern Europe and the mountainous regions of 

 the central and southern parts of the continent are 

 of glacial origin, while the accumulations outside 

 of those areas are chiefly tluviatile. The latter 

 were for some time believed to lie upon the whole 

 younger than the former, but the two series are 

 now generally recognised to lie contemporaneous. 

 The occurrence of fossiliferous lieds intercalated 

 between sheets of morainic matter (lioulder-clay, 

 &c.) proves that the so-called glacial period was 

 interrupted more than once by epochs of milder 

 climatic conditions, during which the inland ice 

 of the north retired from all the low grounds, while 

 the great glaciers of the Alps, \c. Hurak back to 

 the inner recesses of the mountains. The organic 

 remains obtained from fresh-water interglacial 

 dejMwits have been correlated with those which 

 occur in the river-accumulations of the non- 

 glaciated tracts, and the result is that these 

 accumulations are now admitted to lie for the most 

 part of interglacial age also. In short, the peat, 

 river-deposits, tufas, and cave-accunmlations are 

 the equivalents in time of the glacial and inter- 

 glacial deposits. 



Life of the Period. The plants and animals of 

 the Pleistocene betoken great changes of climate 

 one series indicating an extremely cold or Arctic 

 climate, while the other could only have domiciled 

 under extremely clement ami uniform conditions. 

 While a colil climate prevailed, such plants as 

 Dri/a.i nrtii/i'tn/ti. I'.ilnln iniiin. Xufi.f /in/nrix. iVc. 

 tlourished in the plain- of (icrmany, ami similar 

 northern ami Arctic forms clothed the low grounds 

 of Switzerland. In northern France grew birch, 

 alder, larch, spruce, juniper, and yew, while in 

 Northern Italy the Cembran pine flourished in the 

 neighlmiirhood of Ivrea, and the Scotch fir on the 

 shores of Lake Varese, positions in which it is 

 needless to say they could not live now. Contem- 

 poraneous with this flora we meet with land and 

 fresh-water shells which are equally indicative of 

 cold and ungenial conditions. And the same tale 



