ckle-shaped sandbar extending across the narrow
channel.[809] Nature is working in its leisurely way to attach Sakhalin to
the Siberian coast. The strong marine current which sets southward from
the Okhotsk Sea through the Strait of Tartary carries silt from the
mouth of the heavy laden Amur River, and deposits it in the "narrows" of
the strait between Capes Luzarev and Pogobi, building up sandbars that
come dangerously near the surface in mid channel.[810] Here the water is
so shallow that occasionally after long prevailing winds, the ground is
left exposed and the island natives can walk over to Asia.[811] The close
proximity of Sakhalin to the mainland and the ice bridge covering the
strait in winter rob the island of much of its insular character and
caused it to pass as a peninsula until 1852. Yet that five-mile wide
stretch of sea on its western coast determined its selection as the
great penal station of the Russian Empire. The fact that peninsular
India accords in so many points of flora, fauna and even primitive
ethnic stock with Madagascar and South Africa, indicates its former
island nature, which has been geographically cloaked by its union with
the continent of Asia.

[Sidenote: Character of insular flora and fauna.]

Islands, because of their relatively limited area and their clearly
defined boundaries, are excellent fields for the study of floral,
faunal, and ethnic distribution. Small area and isolation cause in them
poverty of animal and plant forms and fewer species than are found in an
equal continental area. This is the curse of restricted space which we
have met before. The large island group of New Zealand, with its highly
diversified relief and long zonal stretch, has only a moderate list of
flowering plants, in comparison with the numerous species that adorn
equal areas in South Africa and southwestern Australia.[812] Ascension
possessed originally less than six flowering plants. The four islands of
the Greater Antilles form together a considerable area and have all
possible advantages of climate and soil; but there are probably no
continental areas equally big and equally favored by nature which are so
poor in all the more highly organized groups of animals.[813] Islands
tend to lop off the best branches. Darwin found not a single indubitable
case of terrestrial mammals native to islands situated more than three
hundred miles from the mainland.[814] The impoverishment extends
therefore to quali