Boundaries.
The northern boundary of Asia is formed by the Arctic Ocean; the
coast-line falls between 70 deg. and 75 deg. N., and so lies within the
Arctic circle, having its extreme northern point in Cape
Sivero-Vostochnyi (i.e. north-east) or Chelyuskin, in 78 deg. N. On the
south the coast-line is far more irregular, the Arabian Sea, the Bay of
Bengal, and the China Sea reaching about to the northern tropic at the
mouths of the Indus, of the Ganges and of the Canton river; while the
great peninsulas of Arabia, Hindostan and Cambodia descend to about 10
deg. N., and the Malay peninsula extends within a degree and a half of
the equator. On the west the extreme point of Asia is found on the shore
of the Mediterranean, at Cape Baba, in 26 deg. E., nor far from the
Dardanelles. Thence the boundary passes in the one direction through the
Mediterranean, and down the Red Sea to the southern point of Arabia, at
the strait of Bab-el-Mandeb, in 45 deg. E.; and in the other through the
Black Sea, and along the range of Caucasus, following approximately 40
deg. N. to the Caspian, whence it turns to the north on a line not far
from the 60th meridian, along the Ural Mountains, and meets the Arctic
Ocean nearly opposite the island of Novaya Zemlya. The most easterly
point of Asia is East Cape (Vostochnyi, i.e. east, or Dezhnev), in 190
deg. E., at the entrance of Bering Strait. The boundary between this
point and the extremity of the Malay Peninsula follows the coast of the
Northern Pacific and the China Sea, on a line deeply broken by the
projection of the peninsulas of Kamchatka and Korea, and the recession
of the Sea of Okhotsk, the Yellow Sea, and the Gulfs of Tongking and
Siam.
Islands.
On the east and south-east of Asia are several important groups of
islands, the more southern of which link this continent to Australia,
and to the islands of the Pacific. The Kurile islands, the Japanese
group, Luchu, Formosa and the Philippines, may be regarded as
unquestionable outliers of Asia. Between the islands of the Malay
archipelago from Sumatra to New Guinea, and the neighbouring Asiatic
continent, no definite relations appear ever to have existed, and no
distinctly marked boundary for Asia has been established by the old
geographers in this quarter. Modern science, however, has indicated a
line of physical separation along the channel between Borneo and
Celebes, called the Straits of Macassar, which follows approximately
120 deg. E., to the west of which the flora and fauna are essentially
Asiatic in their type, while to the south and east the Australian
element begins to be distinctly marked, soon to become predominant. To
this boundary has been given the name of Wallace's line, after the
eminent naturalist, A.R. Wallace, who first indicated its existence.
Form of continent.
Owing to the great extent of Asia, it is not easy to obtain a correct
conception of the actual form of its outline from ordinary maps, the
distortions which accompany projections of large spherical areas on a
flat surface being necessarily great and misleading. Turning, therefore,
to a globe, Asia, viewed as a whole, will be seen to have the form of a
great isosceles spherical triangle, having its north-eastern apex at
East Cape (Vostochnyi), in Bering Strait; its two equal sides, in length
about a quadrant of the sphere, or 6500 m., extending on the west to the
southern point of Arabia, and on the east to the extremity of the Malay
peninsula; and the base between these points occupying about 60 deg. of
a great circle, or 4500 m., and being deeply indented by the Arabian Sea
and the Bay of Bengal on either side of the Indian peninsula. A great
circle, drawn through East Cape and the southern point of Arabia, passes
nearly along the coast-line of the Arctic Ocean, over the Ural
Mountains, through the western part of the Caspian, and nearly along the
boundary between Persia and Asiatic Turkey. Asia Minor and the
north-western half of Arabia lie outside such a great circle, which
otherwise indicates, with fair accuracy, the north-western boundary of
Asia. In like manner a great circle drawn through East Cape and the
extremity of the Malay peninsula, passes nearly over the coasts of
Manchuria, China and Cochin-China, and departs comparatively little from
the eastern boundary.
General physiography.
Asia is divided laterally along the parallel of 40 deg. north by a
depression which, beginning on the east of the desert of Gobi, extends
westwards through Mongolia to Chinese Turkestan. To the west of
Kashgar the central depression is limited by the meridional range of
Sarikol and the great elevation of the Pamir, of which the Sarikol is
the eastern face. The level of this depression (once a vast inland
sea) between the mountains which enclose the sources of the Hwang-ho
and the Sarikol range probably never exceeds 2000 ft. above sea, and
modern researches tend to prove that in the central portions of the
Gobi (about Lop Nor) it may be actually below sea-level. A vast
proportion of the continent north of this central line is but a few
hundred feet in altitude. Shelving gradually upward from the low flats
of Siberia the general continental level rises to a great central
water-parting, or divide, which stretches from the Black Sea through
the Elburz and the Hindu Kush to the Tian-shan mountains in the Pamir
region, and hence to Bering Strait on the extreme north-east. This
great divide is not always marked by well-defined ranges facing
steeply either to the north or south. There are considerable spaces
where the strike, or axis, of the main ranges is transverse to the
water-parting, which is then represented by intermediate highlands
forming lacustrine regions with an indefinite watershed. Only a part
of this great continental divide (including such ranges as the Hindu
Kush, Tian-shan, Altai or Khangai) rises to any great height, a
considerable portion of it being below 5000 ft. in altitude. South of
the divide the level at once drops to the central depression of Gobi,
which forms a vast interior, almost waterless space, where the local
drainage is lost in deserts or swamps. South of this enclosed
depression is another great hydrographic barrier which parts it from
the low plains of the Amur, of China, Siam and India, bordered by the
shallows of the Yellow Sea and the shoals which enclose the islands of
Japan and Formosa, all of them once an integral part of the continent.
This second barrier is one of the most mighty upheavals in the world,
by reason both of its extent and its altitude. Starting from the Amur
river and reaching along the eastern margin of the Gobi desert towards
the sources of the Hwang-ho, it merges into the Altyn-tagh and the
Kuen-lun, forming the northern face of the vast Tibetan highlands
which are bounded on the south by the Himalaya. The Pamir highlands
between the base of the Tian-shan mountains and the eastern buttresses
of the Hindu Kush unite these two great divides, enclosing the Gobi
depression on the west; and they would again be united on the east but
for the transverse valley of the Amur, which parts the Khingan
mountains from the Yablonoi system to the east of Lake Baikal.
If we consider the whole continent to be divided into three sections,
viz. a northern section with an average altitude of less than 5000 ft.
above sea, where all the main rivers flow northward to the
Mediterranean, the Arctic Sea, or the Caspian; a central section of
depression, where the drainage is lost in swamps or _hamuns_, and of
which the average level probably does not exceed 2000 ft. above sea;
and a southern section divided between highly elevated table-lands
from 15,000 to 16,000 ft. in altitude, and lowlands of the Arabian,
Indian, Siamese and Chinese peninsulas, with an ocean outlet for its
drainage; we find that there is only one direct connexion between
northern and southern sections which involves no mountain passes, and
no formidable barrier of altitudes. That one is afforded by the narrow
valley of the Hari Rud to the west of Herat. From the Caspian to
Karachi it is possible to pass without encountering any orographic
obstacle greater than the divide which separates the valley of the
Hari Rud from the Helmund _hamun_ basin, which may be represented by
an altitude of about 4000 ft. above sea-level. This fact possesses
great significance in connexion with the development of Asiatic
railways.
Hydrography.
If we examine the hydrographic basins of the three divisions of Asia
thus indicated we find that the northern division, including the
drainage falling into the Arctic Sea, the Aralo-Caspian depression, or
the Mediterranean, embraces an area of about 6,394,500 sq. m., as
follows:--
Sq. m.
Area of Arctic river basins 4,367,000
" Aralo-Caspian basin 1,759,000
" Mediterranean 268,500
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Total 6,394,500