The Arctic peoples regulated their lives by the long day and night in the year; among the tribes in the arid region the place of sunrise was marked on the horizon for each day; the tropical Indians were not so observant, but they worshipped the sun-god above all.
In the most arid regions there is a small growth of green in the rainy season, and a rich display of small wild-flowers, as well as the enormous flower clusters of the yucca, and blooms in pink and orange, crimson, yellow and scarlet of the giant cactus and its fellows.
The Lower Austral zone occupies the greater part of the Southern states, and is divided near the 98th meridian into an eastern humid or Austroriparian area and a western arid or Lower Sonoran area.
The plateau is bleak and inhospitable in the north, barren and arid toward the south, containing great saline depressions covered with water in the rainy season, and broken by ridges and peaks, the highest being the Cerro de Tahua, 17,454 ft.
Of the mountains belonging to the table-land the most continuous are those of the Cantabrian chain, which stretches for the most part from east to west, parallel to the Bay of Biscay, btit Mountains, ultimately bends round towards the south between Leon and Galicia (see CANTABRIAN MOUNTAINS) - A peculiar feature of this chain, arid of the neighboring parts of the table-land, is the number of the parameras or isolated plateaus, surrounded by steep rocky mountains, or even by walls of sheer cliff.
It is a region of lakes and morasses, of arid plains and high temperatures, but experiments with irrigation toward the end of the 19th century were highly successful and considerable tracts have since been brought under cultivation.
Dukhn, a species of millet which can grow in the arid northern districts is there the chief grain crop, its place in the south being taken by durra.
This phenomenon occurs among species found at high elevations, among others found in arid or desert regions, and in some cases in the female sex only, the male being winged and the female wingless.
The immediate environs are very fertile and produce a great variety of fruits, including many of the temperate zone, but the surrounding country is arid and sterile, producing scanty crops of barley, Indian corn and pease.
The loose material may, and in an arid region does, consist only of portions of the higher parts of the surface detached by the expansion and contraction produced by heating and cooling due to radiation.