The fauna presented likewise evidence that the climate, during at least the earlier part of the Pliocene period, still continued warm enough to permit tribes of animals to roam over Europe,

FIG. 201.-Pliocene Plants. (A) Populus canescens; (B) Salix alba; (C) Glyptostrobus europaus; (D) Alnus glutinosa; (E) Platanus aceroides (all natural size except E, which is ).

the descendants of which are now confined to regions south of the Mediterranean basin. Some of the huge mammalian types that had survived from an earlier time now died out; such was the

case with the deinotherium and mastodon. Herds of pachydermatous animals formed a distinguishing feature of the faunarhinoceroses, hippopotamuses, and elephants, with troops of herbivorous quadrupeds gazelles, antelopes, deer, giraffes, horses, oxen, and strange long-extinct types linking together genera that are now quite distinct. There were, likewise, carnivores (wild-cats, bears, hyænas, etc.), and many monkeys. The remains of monkeys have been found fossil in Europe 14° farther north than their descendants now live.

The shells of the Pliocene deposits afford important evidence regarding the gradual change of climate. The great majority of

FIG. 202.-Pliocene Marine Shells. (a) Rhynchonella psittacea (natural size); (b) Panopaa norvegica (); (c) Purpura lapillus (); (d) Trophon antiquum (3).

them belong to still living species (Fig. 202). They consequently supply an excellent basis for comparison with the existing distribution of the same species. When the deposits containing them are examined with reference to the present habitats of the species, it is found that the percentage of what are now northern shells increases from the lower to the higher parts of the series. In Pliocene time, each species no doubt flourished only in that part of the sea where it found its congenial temperature and food.

We infer that its requirements are still the same at the present day, in other words, that the temperature of the regions within which the species is now confined afford, on the whole, an indication of the temperature of the areas within which it lived in the Pliocene seas. On this basis of comparison, the inference has been drawn that the climate in the northern hemisphere, after becoming temperate, passed on to a more rigorous stage. In the end thoroughly Arctic conditions spread over most of Europe and a large part of North America, during the period that succeeded the Pliocene (p. 352).

In Britain Pliocene deposits are almost entirely confined to the counties of Norfolk and Suffolk. They consist of various shelly sands, gravels, and marls, which have long been known as "Crag." Arranged in descending order, the following are the recognised subdivisions ::

Forest-Bed Group

Chillesford Group

Norwich (fluviomarine or mammaliferous) Crag

Upper fresh-water, estuarine, and Lower fresh-water sands and silts, with layers of peat, having a total depth of 10 to 70 feet. Among the terrestrial plants are cones of Scotch fir (Pinus sylvestris) and spruce (Abies), leaves of water-lily (Nymphæa alba), yellow pond-lily (Nuphar luteum), hornwort (Ceratophyllum), blackthorn (Prunus spinosa), bog-bean (Menyanthes trifoliata), oak, and hazel, with land and fresh-water shells, and many mammals, including species of wolf, fox, machairodus, hyæna, glutton, bear, seal, horse, rhinoceros, hippopotamus, pig, ox, musk-sheep, deer, beaver, trogontherium (a huge extinct kind of beaver), mole, elephant (E. antiquus, E. meridionalis, E. primigenius), etc. This group of strata is found at the base of the sea-cliff of boulder-clay in Norfolk, and extends under the present

sea.

Sands and clays occurring as a thin local deposit in Suffolk, 6 to 16 feet thick, with marine shells, about two-thirds of which still live in Arctic waters (Mya truncata, Cyprina islandica, Astarte borealis, Tellina obliqua).

Shelly sand and gravel, 5 to 10 feet thick, containing 93
per cent of still living species of shells and bones
and teeth of mastodon, elephant (E. meridionalis, E.
antiquus), hippopotamus, rhinoceros, etc.
The pro-
portion of northern shells is 14.6 per cent, and the
following species are included—Rhynchonella psittacea,
Scalaria grænlandica, Panopea norvegica, Astarte
borealis. About twenty species of land or fresh-water
shells also occur.

Red Crag

Lenham Beds (Diestian)

St. Erth Beds

White (Suffolk or
Coralline) Crag

A local and inconstant accumulation, 25 feet thick, of red and dark brown ferruginous shelly sand, with numerous species of shells of which 10.7 per cent are northern forms. Some of the characteristic shells of the deposit are- ·Trophon antiquum, Voluta Lamberti, Purpura lapillus, Pectunculus glycimeris, Cardium edule.

Sands and ironstones filling hollows of the Chalk of the North Downs, more than 600 feet above the sea, and containing nearly 200 species of fossils, all of which, save 22, have been found in the Coralline Crag.

A local deposit of clays and gravels found at St. Erth in Cornwall, with abundant and well-preserved shells, probably of older Pliocene age, about 40 per cent being of extinct species.

Shelly sands and clays containing 84 per cent of still living shells, whereof 5 per cent are northern species. One of the characteristics of the deposit is the large number (140 species) of coral-like polyzoa (corallines or bryozoa), whence one of the names given to this subdivision.

On the Continent the youngest Tertiary deposits cover comparatively small areas and mark some of the last tracts occupied by the sea. Thus, in the Vienna basin there is evidence that the sea, shut off from the main ocean, and partly converted into an inland sea, like the Caspian, was gradually filled up with sediment and raised into land. Along the northern borders of the Mediterranean Sea, thick masses of marine Pliocene strata show the prolonged depression of that region during Pliocene time, and its subsequent elevation. In the south of France these strata, lying unconformably on everything older than themselves, reach a height of 1150 feet above the sea. Along both sides of the Apennine chain, Pliocene blue marls, clays, and sands, known as the sub-Apennine beds, have been uplifted into a range of low hills. These deposits swell out southwards, reaching their greatest thickness (2000 feet or more) in Sicily, which was probably the region of maximum subsidence during Pliocene time. Here and there, in the Italian strata of this period, remains of terrestrial vegetation and land-animals are abundantly preserved. One of the most noted localities for these fossils is the upper part of the valley of the Arno.

Perhaps the most curious and interesting assemblage of the land-fauna of Europe during Pliocene time has been found in some hard red clays, alternating with gravels, at Pikermi in Attica.

Thirty-one genera of mammals have there been obtained, of which twenty-two are extinct. The ruminants, specially well represented among these remains, include species of giraffe, helladotherium (Fig. 203), antelopes, gazelles, and other forms allied to, but distinct from, any living genera. There are likewise the bones of gigantic wild boars, several species of rhinoceros, mastodon,

FIG. 203.-Helladotherium Duvernoyi (¿)—a gigantic animal intermediate in structure between the giraffe and the antelope, Pikermi, Attica.

deinotherium, porcupine, hyæna, various extinct carnivores, and a monkey.

In India a somewhat similar fauna has been obtained from a massive series of fresh-water sandstones, known as the Siwalik group. A large proportion of the remains belong to existing genera of animals, such as macaque, bear, elephant, horse, hippopotamus, giraffe, ox, porcupine, goat, sheep, and camel. Various extinct types were contemporary with these animals, two of the most extraordinary of them being the Sivatherium and Bramatherium-colossal, four-horned creatures allied to our living antelopes and prong-bucks.