Page:EB1911 - Volume 28.djvu/209

Rh Himalaya, and North America, are divided into genera and subgenera. Examples of some of these are afforded by the English representatives of the group.

The first of these is the common short-tailed field-mouse, or “field-vole,” Microtus agrestis, which belongs to the typical section of the type genus, and is about the size of a mouse, with a short stumpy body, and a tail about one third the length of the head and body. The hind feet have six pads on their inferior surfaces, and the colour is dull grizzled brown above and greyish white below. The molar teeth have respectively 5, 5 and 6 prisms above, and 9, 5 and 3 below. This rodent is one of the commonest of British mammals, and frequents fields, woods and gardens in numbers, often doing considerable damage owing to its fondness for garden produce. It is spread over the whole of Great Britain (exclusive of the Orkneys), while on the continent of Europe its range extends from Finland to North Italy and from France and Spain to Russia.

The second and larger species is the water-rat, or “water-vole,” which belongs to a second section of the genus, and is commonly known as Microtus (Arvicola) amphibius, although some writers employ the inappropriate specific name terrestris. It is about the size of a rat, and has long soft thick fur, of a uniform grizzled brown, except when (as is not uncommon) it is black. The tail is about half the length of the head and body, and the hind feet are long and powerful, although not webbed, and have five rounded pads on their lower surfaces. In the upper jaw the first molar has 5, the second 4 and the third 4 prisms, of which the last is irregular and sometimes divided into two, making 5. In the lower jaw the first molar has 7 prisms, of which the 3 anterior are generally not fully separated from one another, the second 5 and the third 3. The water-rat is perhaps the most often seen of all English mammals, owing to its diurnal habits. It frequents rivers and streams, burrowing in the banks, and often causing considerable damage. Its food consists almost wholly of water-weeds, rushes and other vegetable substances, but it will also eat animal food on occasion, in the shape of insects, mice or young birds. The female has during the summer three or four litters, each of from two to seven young. The range of the water-rat extends over Europe and North Asia from England to China, but the species is not found in Ireland, where no member of the group is native.

The red-backed field-mouse or “bank-vole” may be distinguished externally from the first species by its more or less rusty or rufous-coloured back, its larger ears and its comparatively longer tail, which attains to about half the length of the head and body. On account of an important difference in the structure of its molars, it is now very generally referred to a distinct genus, under the name of Evotomys glareolus; these teeth developing roots at a certain stage of existence, instead of growing permanently. Their prisms number respectively 5 and 4 and 5 above, and 7, 3 and 3 below. The habits of this species are in every way similar to those of the one first on the list. Its range in Great Britain extends northwards to Morayshire, but it is represented in an island off the Pembroke coast by a distinct form; on the continent of Europe it extends from France and Italy to southern Russia, while it is represented in northern Asia and North America by closely allied species. Fossil voles from the Pliocene of England and Italy with molars which are rooted as soon as developed form the genus Mimomys.

 VOLGA (known to the Tatars as Etil, Itil or Atel; to the Finnish tribes as Rau, and to the ancients as Rha and Oarus), the longest and most important river of European Russia. It rises in the Valdai plateau of Tver and, after a winding course of 2325 m. (1070 in a straight line), falls into the Caspian at Astrakhan. It is by far the longest river of Europe, the

Danube, which comes next to it, being only 1775 m., while the Rhine (760 m.) is shorter even than two of the chief tributaries of the Volga—the Oka and the Kama. Its drainage area, which includes the whole of middle and eastern as well as part of south-eastern Russia, amounts to 563,300 sq. m., thus exceeding the aggregate superficies of Germany, France and the United Kingdom, and containing a population of fifty millions. Its tributaries are navigable for an aggregate length of nearly 20,000 m. The “basin” of the Volga is not limited to its actual catchment area. By a system of canals which connect the upper Volga with the Neva, the commercial mouth of the Volga has been transferred, so to speak, from the Caspian to the Baltic, thus making St Petersburg, the capital and chief seaport of Russia, the chief port of the Volga basin as well. Other less important canals connect it with the Western Dvina (Riga) and the White Sea (Archangel); while a railway only 45 m. in length joins the Volga with the Don and the Sea of Azov, and three great trunk lines bring its lower parts into connexion with the Baltic and western Europe.

The Volga rises in extensive marshes on the Valdai plateau, where the W. Dvina also has its origin. Lake Seliger was formerly considered

to be the principal source; but that distinction is now given to a small spring issuing beneath a chapel (57° 15′ N.; 32° 30′ E.) in the midst of a large marsh to the west of Seliger. The honour has also been claimed, not without plausibility, for the Runa rivulet. Recent exact surveys have shown these originating marshes to be no more than 665 ft. above sea-level. The stream first traverses several small lakes, all having the same level, and, after its confluence with the Runa, enters Lake Volga. A dam erected a few miles below that lake, with a storage of nearly 10,000 million cub. ft. of water, makes it possible to raise the level of the Volga as far down as the Sheksna, thus rendering it navigable, even at low water, from its 65th mile onwards.

From its confluence with the Sheksna the Volga flows with a very gentle descent towards the south-east, past Yaroslavl and Kostroma, along a broad valley hollowed to a depth of 150-200 ft, in the Permian and Jurassic deposits. In fact, its course lies through a string of depressions formerly filled with wide lakes, all linked together. When the Volga at length assumes a due south-east direction it is a large river (8250 cub. ft. per second, rising occasionally in high flood to as much as 178,360 cub. ft.); of its numerous tributaries, the Unzha (365 m., 330 navigable), from the north, is the most important.

The next great tributary is the Oka, which comes from the south-west after having traversed, on its course of 950 m., all the Great

Russian provinces of central Russia. It rises in the government of Orel, among hills which also send tributaries to the Dnieper and the Don, and receives on the left the Upa, the Zhizdra, the Ugra (300 m.), the Moskva, on which steamers ply up to Moscow, the Klyazma (395 m.), on whose banks arose the middle-Russian principality of Suzdal, and on the right the navigable Tsna (255 m.) and Moksha. Every one of these tributaries is connected with some important event in the history of Great Russia. The drainage area of the Oka is a territory of 97,000 sq. m. It has been maintained that, of the two rivers which unite at Nizhniy-Novgorod, the Oka, not the Volga, is the chief; the fact is that both in length (818 m.) and in drainage area above the confluence (89,500 sq. m.), as well as in the aggregate length of its tributaries, the Volga is the inferior stream.

At its confluence with the Oka the Volga enters the broad lacustrine depression which must have communicated with the Caspian during

the post-Pliocene period by means of at least a broad strait. Its level at low water is only 190 ft. above that of the ocean. Immediately below the confluence the breadth of the river ranges from 350 to 1750 yds. There are many islands which change their appearance and position after each inundation. On the right the Volga is joined by the Sura, which drains a large area and brings a volume of 2700 to 22,000 cub. ft. of water per second, the Vetluga (465 m. long, of which 365 are navigable), from the forest-tracts of Yaroslavl, and many smaller tributaries. Then the stream turns south-east and descends into another lacustrine depression, where it receives the Kama, below Kazañ. Remains of molluscs still extant in the Caspian occur extensively throughout this depression and up the lower Kama.

The Kama, which brings to the Volga a contribution ranging from 52,500 to 144,400 cub. ft. and occasionally reaching 515,000 cub. ft. per second, might again be considered as the more important of the two rivers. It rises in Vyatka, takes a wide sweep towards the north and east, and then flows south and south-west to join the Volga after a course of no less than 1150 m. 