marine origin in California are those of San Diego and Wild Cat. In the Rocky Mountains are large lacustrine formations of considerable thickness, and certain conglomerates in Wyoming and Bishop Mountain arc assigned to this age. The sands and clays with gypsum of Entre Rios in South America contain fossils of the Atlantic type.
Lignitiferous shale with petroleum and great thickness of volcanic tuffs have been found in southern Sumatra. In New South Wales Pliocene river terraces and alluvial deposits are covered by Mid- Pliocene lavas and from these " deep leads " or buried river beds much gold has been obtained. In Victoria great basaltic and doleritic flows have filled up the Pliocene river valleys, and marine beds have been found at elevations of 1000 ft. above present sea-level. Very similar deposits and volcanic rock, belonging to the Wanganui system of F. W. Hutton, are found in New Zealand.
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TABLE OF PLIOCENE FORMATIONS.
Stages.
England.
Belgium
and Holland.
Rhone Basin.
Languedoc
and Roussillon.
Italy.
Eastern Europe.
Other Countries
Sicilian.
Cromer Forest
Bed. Fluvio-marine
Norwic h
crag. Red crag of
Suffolk.
Clays of Campine. Amstelian.
Astian,
Base of Red crag.
Poederlian.
Scaldisian sands with Tropkon antiquum.
Marls of St
Cosme. Gravels of
Chagny. Conglomerates of
Chambaran. Sands of Trc-
voux and
Mollon. Travertine of
Meximieux.
Durfort beds with EUphas nuridionalis.
Sands of Val d'Arno.
Limestones of Paler- mo and clays with northern mollusca.
Paludina (Vivipara)
Marine beds ef Entre Rios.
Volcanic tuffs d Sw Sumatra.
Conglomerates of Montpellicr and Fourrcs.
Sands of Rous- sillon with Ma s lodon arvernensis.
Marls of Val d'Arno with Mastodon arvernensis*
Yellow sands of Asti, Plaisantin, Monte Maria and Tuscany.
Conglomerates of Castrovillari.
Middle Paludina bods.
Petroleum-bearisf beds of Sumatra.
Marine sands U Moghara aad I Mokatta.
Plaisancian.
Coralline crag. Lenham beds.
Sands with Isocardia car. Diestian sandstones.
Marine marls of Brcsse, Hauterivcs.
Congeria beds olBollene.
Yellow sands of Montpellicr.
Blue marls of Millas.
Blue marls of Pia- cenza, Bologna, and Vatican.
Lower Paludina beds.
Marine beds ef
Florida. Lacustrine bed* ef
Rocky
tains.
Life of the Pliocene Period.—Sir C. Lyell denned the Pliocene strata as those which contained from 36–95% of living marine molluscs. This rule can no longer be strictly applied to the widely scattered marine deposits, and it is of course inapplicable to the very numerous formations of lacustrine and fluviatile origin. On the whole the marine organisms are very like their living representatives, and there is often practically no specific difference; Nassa, Valuta, Chenopus, Denmium, Fusus, Area, Peden, Pectunculus, Panopoea, Cyprina and Mactra may be mentioned among the marine genera; Congeria (Dreyssensia), Auricula, Paludina, Meianopsis ana Helix are found in the lacustrine deposits. One of the most interesting facts exposed by the study of the mollusca is the gradual lowering of the temperature of Europe during the period. In Britain the early Pliocene was, if anything, warmer than at present, but the percentage of northern forms ascends steadily through the higher beds, and finally arctic forms, such as Buccinum groenlandicum, Trichopteris borealis, Mya truncata, Cyprina islandica, &c, appear on the coasts of Norfolk and Suffolk, and some of the northern species even reached the Mediterranean (Sicily) at the close of the period. The flora exhibits the same gradual change, the large palms and camphor trees disappeared from Europe, the sabal palm lingered in Languedoc, and Chamerops humilis lived about Marseilles until the end; the sequoias and bamboos held on for some time, and the aspect of the vegetation in mid-Pliocene times was not unlike that of Portugal, Algeria and Japan of to-day. Not a few species that dwelt in Pliocene Europe are found in the forests of America. The flora of the Cromer forest beds is very like that of the same district at the present time. The mammals of the British Pliocene show a curious blending of northern and southern forms; they include Machaerodus (the sabre-toothed lion), hyenas, dogs, fox, wolf, glutton, marten, bears, Ursus arvernensus and the grizzly and cave bear, seals, whales, dolphins, bisons, musk ox, gazelle, the red deer and many others now extinct, the roebuck, pigs and wild boar, hippopotamus, hipparion and horse (Equus caballus and E. stenosis), several species of rhinoceros, tapir, hyrax, elephants (Elephas meridionalis and E. antiques), several mastodons, squirrel, beaver, hare, mice, voles, &c. The mastodon disappeared from Europe before the close of the period, but lived much longer in America. No generally accepted fossil man has been found in the Pliocene; Pithecanthropus erectus, found by E. Dubois in Java, is the nearest to the human type. Monkeys, Macacus and Semnopithecus, occur in the Pliocene of Europe. At this time the Pliocene mammals of North America were able to migrate into South America, and a few Of the southern forms travelled northwards.
See C. Reid, " The Pliocene Deposits of Britain " (Mem. Geol. Survey, 1890); E. T. Newton, " The Vertebrates of the Pliocene Deposits of Britain " (Mem. Geol. Survey, 1891) (both contain a bibliography): C. Reid, Origin of the British Flora (1899); and " Geological Literature " (Geol. Sec. London Annual, since 1893). (J. A. H.)
PLOCK, or Plotsk, a government of Russian Poland, on the right bank of the Vistula, having the Prussian provinces of
West and East Prussia on the N. and the Polish governments
of Lomza on the E. and Warsaw on the S. Its area is 4160 sq. m.
Its flat surface, 350 to 500 ft. above the sea-level, rises gently
towards the north, where it merges into the Baltic coast-ridge
of the Prussian lake district. Only a few hills reach 600 ft. above
the sea, while the broad valley of the Vistula has an elevation
of only 130 to 150 ft. In the west (district of Lipno) broad
terraces, covered with forests, small lakes and ponds, and very
poor in vegetation, descend from the Baltic lake-district towards
the plains of Plock; and in the central district of Mlawa extensive
marshes fill the upper basin of the Wkra. The Vistula borders
the government on the south, almost all the way from Warsaw
to Thorn, receiving the Skrwa and Wkra. The Drwęca, or
Drewenz, flows along the north-west boundary, while several
small tributaries of the Narew drain the north-eastern district
of Ciechanow. Peat-bogs, used for fuel, and marshes containing
bog-iron, fill many depressions in the north, while the more
elevated parts of the plains are covered with fertile clays, or a
kind of "black earth." Lacustrine post-Glacial deposits fill
all the depressions of the thick sheet of boulder clay, with
Scandinavian erratic boulders, which extends everywhere over
the Tertiary sands and marls—these last containing masses of
silicated wood and lignite. Layers of gypsum are found in the
hills beside the Vistula.
The estimated population in 1906 was 619,000. About one-third are Jews and 36,000 Germans. The government is divided into seven districts, of which the chief towns are Plock, Ciechanow, Lipno, Mlawa, Prasnysz, Rypin and Sierpc. Agriculture is the chief industry. The principal crops are rye, oats, barley, wheat and potatoes; beetroot is cultivated for sugar, especially on the large estates of the west, where modern machinery is used. Gardening and bee-keeping are extensively practised. In the north the property is much divided, and the landholders, very numerous in Ciechanow, are far from prosperous. The forests have been lavishly cut, but Plock is still one of the best wooded governments (20%) in Poland. Other occupations are provided by shipping on the Vistula, mining and various domestic industries, such as the fabrication of wooden cars, sledges and wheels, and textile industry. The manufactures include flour-mills, saw-mills, sugar factories, distilleries, tanneries, breweries,
